How can I prove ownership of my vehicle?

Step one:

Prove ownership. This takes getting the executor of the estate to sign paper work attesting to you being the legal owner. Even if it was willed to you or you are the executor the title along with supporting documents (that show grandpa did in fact die and that the executor has agreed that the car belongs to you).

Step two:

Have the vehicle removed from impound. This can be done by having it towed to a place that is off the street, secure and legal. In some places cars can not be left on lawns or if not registered in sight.

Step three:

This one is a bit tricky, in some states a person has to have the vehicle pass inspection first before it can be registered, if this is the case the car should be towed to a garage that can perform the inspections. Some states allow for the vehicle to be operated for a few days before it has to be inspected. Either way the next thing is to get it registered and to do that you need insurance.

IF you have the title, signed over by anyone that legally CAN sign it over, you have ALL the proof possible.

You NEVER need the registration to claim a car with proof of ownership, which the title IS.

Your story literally CANNOT be accurate.

You'll have to take the Will to the DMV, your signature means that you stole it.

It isn't your car.  An  inherited car is not your car until you do the paperwork and there is a specific way they do it. They have the rules and you follow them. You don't need the car, you need the old paperwork in the glovebox.  They (for me it is all done at an insurance agent - you however MAY have to go to DMV.By foot-mobile. Insurance agents are closer most likely so I would try them first.  Then when the car paperwork is done and you bought insurance even 1 way insurance(drive from point A to point B)ONLY; that is good enough to get it out of the impound yard.  You will also have to pay the impound yard for the Towing there and the Daily Impound Fee FIRST before you can get the car. Then you can drive it home and park it IN THE YARD.

. Now you need car insurance before you drive it out of the yard.  Then you phone and make an appointment for an Inspection. If you fail the inspection, you have a period of time to get it fixed and bring it back for another inspection. If you pass, then you get a piece of paper to prove it was inspected. Until next time.

. It takes longer to write this than actually do it.

You bring the signed title to the government agency that issues titles and pay a fee to exchange it for a new title with your name.

Why do young adults insist to ignore important aspects of the law?  Do you think that police and other governmental officials will let you break laws and then just give you a warning, like your parents have obviously done? 

If your grandfather died, there may be a way in your state to easily get title to his car.  Otherwise probate court is necessary. 

A general warning for you and others:  you can NOT sign someone else's name to a legal document (like a car title) unless you have lawful "power of attorney".  Do some research on this. 

By all the slippery logic in your question, you really know nothing about car ownership. 

If you "inherited" his car, then a probate court will give you title to his car.  Your mother can't just give you an unsigned title and the keys to the car.  Then you certainly can't just drive the car! 

So right now, you need to establish ownership of the car.  You can ask your local DMV for advice.  You can ask the "executor" of your grandfather's estate to get you title.  Or you must have a hearing in a county probate court to obtain title. 

Now that the car is impounded, and you've likely wasted a few weeks doing nothing, you may not be able to afford to pay the towing and storage fees of the car.  The towing company can probably auction the car after 30 days, to recover their "costs". 

After you get title, you can get the car released from car jail. 

Then you get insurance. 

Then you can get it "registered".  That means license plate(s).

Where are you located anyway. 

Do you have a driver's license? 

You'll probably lose the car because of the way you did things. 

P.S.  You mistakenly state that you must get it registered to get it out.  That's not true. 

You correctly state that you "need to prove ownership to retrieve it".  That's true.  You show ownership with your name on a title.  So you need to get the title transferred to your name.  It's that simple. 

Of course they won't let you drive it away unless you have insurance and license plates.  The towing company is like a mini police station.  They make lots of money from situations like yours, plus they force revenue for the state.  You can tow it away without insurance or registration.  Likely they will deliver it to your house for $75.  If you get that far, do not let the car sit on the street without a license plate on it, or they will take it again.  Keep it in your back yard. 

Simple answer to your question: 

You prove ownership by establishing ownership.  Your name on a title.  The receipt of title application/transfer from the DMV will be sufficient.  Many state's DMV have quick title services.  Do that.  Don't wait for a title in the mail. 

If you have proper paperwork and the towing company won't release the car to you, call the city police or county sheriff to assist you! 

How do they calculate the fee due?  $75 towing fee plus how much storage charge per calendar day?  $25?  $35?  $50??  It's easy to get a $500 bill by wasting time. 

I once had my car towed and impounded for less than 12 hours (2 calendar days) the towing fee and 2 days storage fee plus a pile of state fees it cost $250!!  I had a valid driver's license, insurance and registration and it still cost that much!  Why did they impound my vehicle?  The taillights were out at night because of a headlight switch defect and I didn't know it.

Its going to vary a lot depending on where you live but a title with your name on the back and a bill of sale should be enough.

the problem is while waiting for a new title, your car is accruing daily storage fees. Which if are not paid mean losing the car to the storage lot in lieu of the fees.

So You will have to get Grandpa's executor to sign the title over to you.  So then you will have to get a new title in your name and buy license plates and buy insurance.  So get all that done and maybe, just maybe you can get the car out of impound. 

 So.  What goes around, comes around.  

So When you find yourself in a hole, stop digging !

The "SO" generation;  They run their lives about the same as they write.

So......  Grammar matters

You must have been driving the car without legit registration. It's funny how the cops can magically detect that. You'll need your grandpa's title signed over to you (by the executor of his estate) and then you need to get your own title from the DMV and your own registration, which will probably require expensive insurance up front. They should release the car to you without a safety inspection. You will have to pay big storage fees, though, to get the car released. You might want to decide how much the car is worth to you. It might be a good idea to abandon it.

Looks like you are screwed.