Can i clean this?

You can try a melamine sponge. On the other hand, helmets are the one item you always buy new. You don’t have to buy the $300 model, but you also don’t want to save a little time and risk your brain.

For sure.

Get some 99% isopropyl alcohol, and it should take it off. Also good thing to have in your cleaning kit anyway, and useful for things like light cleaning brake discs etc.

Start with soft cloth, but you might need the help of something like a non-scratch dish sponge.

And worst case, get some cool decals / stickers.