Dave,
I'm afraid that the answers to your question, including mine, were not supported by any facts. So, I searched through Tom Grinslade's book on fowlers and came up with the following;
In the New England section, there are 21 fowlers that are signed by the maker. Sixteen are signed on the lock, five on the barrel. Of the five signed on the barrel, all but one are 19th century guns. The other one is dated 1797. Of the 16 signed on the lock , all are 18th century, most being Rev War and before. The names of those signing on the lock are Allen, Manning, Waldren, Pomeroy, Earl, Johnson, Barrett, Sawyer, White Wille, and Hills. In addition, I have four maker signed COS type muskets. One is signed M. Hills on the Dutch musket lock, one is marked Johnson on the typical Worchester/Sutton French type lock, one is marked S. Barrett inside the French 1742 musket lock, and one is marked on the English trade lock (just got this one and doing more research at he present time.) I also just sold a John Hills flintlock pistol- signed on the lock. I believe there was a Thomas Holbrook pistol sold recently, also signed on the lock.
So, if your question is concerning a Rev War, Lexington/Concord type fowler, then it would be most appropriate to sign it on the lock.
Tony- It appears that the locks that are signed by the fowler makers appear to be not made by the maker but most appear to be European.
Al