Yes. The technical requirements for a piece of commercial paper---sometimes called a "negotiable instrument," or a check---are that it be a writing, payable to

Yes. The technical requirements for a piece of commercial paper---sometimes called a "negotiable instrument," or a check---are that it be a writing, payable to the order of someone specific or simply the bearer, that it be signed by the maker or drawer, that it be for a sum certain, that it be unconditional, that it be payable on demand, and that it be payable in currency. Technically, you can make a valid check out of a napkin with a Sharpie.