There are all kinds of solvents you can use to remove graffiti. If you go into a good hardware store or a Home Depot, you will see a dizzying array of things that claim they get rid of all kinds of graffiti and glues.
The most important thing to remember is this: most don’t work very well.
I have found that you need to carry only two solvents:
Goof-off is great for sticker glue, some markers, crayons and pastels, and white marker on black posts. It is not nearly as toxic as the stronger version, and you want to use this whenever you can. It works great on stickers and you will be using this and a razor blade a lot to get rid of those.
There is a stronger version of Goof-off that I tried two months ago, and never looked back. The stuff is great. You don’t want to get it on your skin or breath it in, but it isn’t is toxic as many others.
Using it isn’t simple. You need to use some really good disposable cloths. You can’t use household paper towels, as they are too weak, and you can’t use real rags, as you need too many. Home Depot sells wonderful disposable super-strong paper towels for $10 for a box of 200. They are the greatest thing ever.
Using this stuff isn’t simple. You have to spray an area, and then rub it almost immediately. If you wait 10 seconds, the stuff isn’t as effective. I don’t know why.
Also, it might seem like it isn’t working at first, then after 10 scrubs, it suddenly makes a big difference. The key test is this: if on the first scrub, absolutely none comes off on the cloth, it won’t work. If a little comes off, then you can probably get the rest off with effort.
It sounds strange, but you will need practice with the goof-off and the cloths to get more effective at removal.