The following rules apply to your inquiry: 1.21. Do not indirectly or directly refer to your signature block, suggest looking at your signature block, or include your content signature or signature block in any post; instead, use the signature block feature. Exceptions may be made if your signature is short and relevant or short and benign (e.g., your first name with no catch phrases and no domain names), especially in the marketplace and direct messages where content signatures are generally allowed.
If you wish to rent your signature out, that's your choice. Your signature is your personal advertising and message area. You may use it for whatever you want as long as the signature complies with all the rules referenced above.