Can a handwritten note from an individual be considered a legal document if it does not have an attorney's or courts stamp or signature?

Contracts can be handwritten; they could even be scrawled on the back of an envelop or cocktail napkin and be enforceable. Except for a very few special types of documents (like wills), there is no particular requirement for witnesses, stamps, seals, etc. All a written contract needs is that it is signed by both parties. Contracts can even be formed verbally without any writing--in that case, if one party makes an offer and the other clearly accepts it, that's a contract.