There are four elements of a contract:
Offer - "Have $10k for referring employees."
Acceptance - "Here is an employee."
Intent - "Have $10k"
Consideration - "$10k" -> "refer employee"
The OP's case is even stronger if he sent an email back saying "Thanks for offering $10k! I have a friend who would be interested!" as that is clear acceptance.
Signatures aren't needed (there's plenty of case law around). Courts are more likely to get involved where money is involved, as that shows firm commitment to a contract.
I am not a lawyer, this isn't legal advice, of course.
The OP's case is even stronger if he sent an email back saying "Thanks for offering $10k! I have a friend who would be interested!" as that is clear acceptance.
Signatures aren't needed (there's plenty of case law around). Courts are more likely to get involved where money is involved, as that shows firm commitment to a contract.
I am not a lawyer, this isn't legal advice, of course.