I have a big whiteboard in my room, and I'm getting friends

>>1159671
the whiteboard is most likely made from melamine. if you want to find a professional way to seal that material, a google search is a click away. With that being said, clear spray paint would probably work

I'm assuming you're getting them to sign it with a "permanent" marker like a Sharpie.

A spray can of clear coat wouldn't work since the solvents in it would diffuse the markings and make it ugly.

I suggest taping over the whiteboard with a large sheet of 2-4mil clear adhesive vinyl.

Have you considered having the people sign a poster board or canvas? Those are much better mediums.

>decent camera + tripod
>frame the shot and take a HQ picture of the board
>save a copy in the cloud + backups
>resize it to desired size and send it in to get printed as a poster
>frame it if so desired

boom

How about they sign a large piece of paper instead?

>>1159671
Just give them sharpies not dry erase markers