Your sellers may be required by law to fill out a seller's disclosure, but buyers are not required to sign the disclosure. Even though the Texas REALTORS® Seller's disclosure notice (TXR 1406) and the TREC Seller's Disclosure Notice (TREC OP-H) provide places for a buyer to sign on the last page, a buyer does not have to sign or initial at all.
The lines for the buyer are there, however, because obtaining a buyer's signature is one way for a seller - and the seller's agent - to prove that the buyer received a copy of the seller's disclosure. And, for that reason, some brokerages make it office policy for listing agents to attempt to get buyer's signatures. Keep in mind that a buyer's signature indicates nothing except that the buyer acknowledges receiving the disclosure.
Whether buyers sign or do not sign your seller's disclosure, it's a good idea to note in the transaction file when the buyer was given the disclosure notice.