Is it illegal to enter an abandoned home or building?

Yes.~

The signs are just there to remind you. If there is no sign, it is still trespassing and you can still be arrested for going onto someone else's property. There is no such thing as "un-owned" property. Even if the building is falling down, it is owned by someone.

extremely all you will desire to do is be sure you have adequate gas to make it out. Then stress around for a on a similar time as. you will see abandoned builings. Burnt out structures. broken abode windows. greater burnt out issues. drug sellers, prostitutes. a great number of filled animal memorials scattered around. the city is in actuality packed with dying and rot. no longer my widespread place as you are able to tell. Oh, and in the experience that your gonna do it, do no longer flow by myself. Have a cell telephone with you. and don't flow at evening. and have a street map with you. reason that's straight forward to get circled. Ya understand, there is a few %. on Flickr already. a great number of detroit %.. commute the secure way, seem on the %. particularly.

It's still trespassing even if there isn't a sign

Well someone has to own it, even if it is abandoned, so yes, illegal.