can I put a slow moving sign on my 3 wheeler to ride on public roads?

Depends on actual 3 wheeler and state laws in state of residence. A few of the older 3 wheelers with hitches and farm equipment can be called 'implement of husbandry' and legal to run on a few roads in a few states with a 'slow moving vehicle' triangle like the Amish buggies. My sister runs her Yamaha ATV on roads legally- it has a PTO and sprayer mounted on it- does yours? OR a 3 pt hitch? OR a tiller attached? Brindley hitch and a plow? Sickle bar mower? IF you don't have the needed agriculture equipment, you won't get a pass as a farm vehicle. IF you can do tractor work, in a few states you can get on public road during daylight with the slow moving triangle for slow speed city and county roads- not interstate. Old Cushman trikes with dump box, trailer hitch and some of the later Japanese trikes seen occasionally on road pulling cart full of chicken manure- police don't want to impound them in their garage and driver may be known to them as license pulled drunk driver.

You might be able to pass it as a "farm vehicle" and then you would need flashing lights and a slow moving vehicle sign. If you can't then you could try as a recreational vehicle but that would need head/brake lights, turn signals, license plate ect. Finally you could stay off busy roads and, if your local cops are nice, get away with driving it on the street anyway.

You have a trike, or you have a big-wheel??

Anything you ride on a public street/road has to be street legal. That means light, license plates & drivers license.

Why would the cops not be right??

what did the cops tell you? Did they say you could put a slow moving sign on it or " told me it needs lights, title and bs"? Rather obvious, NO.

No, it won't. Cops will still tell you it needs lights, title, insurance and an operator's license to run it on the streets.

Nope

What did the cops tell you, slick? But you go ahead and ride it on the street until they decide you don't need it anymore.

No. Now that I and every other person that answered has told you not to do it will you try anyway? Get over it. It's illegal. Walk to school.

Is a slow moving light:

Lights?

Title?

Insurance?

etc? NO. So no it wont do it.

Yes, that will make it perfectly legal. You will need to add the word "idiot" to the end of your sign.