Perhaps it was more common in the Midwest, I'm not sure, but I have four rifles that are indeed signed on the underside of the barrel by the gunmaker. Three are by Illinois makers, one is by an Iowa maker. The three Illinois-made rifles are: H. J. DREW DIXON ILL; JAMES DONN CANTON ILL; and S. AVIS. The Iowa-made rifle is the L. W.BABBITT rifle which is on display in our Library here. In the case of both the H. J. DREW and the JAMES DONN rifles, there are other known examples that are signed on the top of the barrel. Why these particular guns were signed underneath remains a mystery. The DONN rifle is not only stamped beneath the forend, it is stamped there at least five times with his usual "JAMES DONN CANTON ILL" one piece stamp. One wonders whether the customer it was made for objected to Donn putting his name on the barrel and Donn was angry about it when he stamped it repeatedly on the underside.
Additionally, I have seen a few others that were stamped on the underside. One was a W. FARRAR GALENA ILL, which is another example by a maker who did it both ways. There was also a maker in Young America, Illinois (now Kirkwood) who signed nearly all of his guns on the underside, sometimes stamped into the wood inside the barrel channel. I recently bought a rifle by C. & F. WUERKER ALTON ILL, which is stamped on top of the barrel, but is also stamped in the wood on the underside of the stock behind the trigger guard. The noted Plains Rifle maker, Stephen O'Dell in Natchez, Mississippi, also stamped his rifles "S. O'DELL NATCHEZ" in the wood behind the trigger guard.
I also have two rifles which are signed in silver inlays in the stock. One of these is one of the two L. G. WARD SPRINGFIELD ILL rifles that are pictured here in the Library. The other is a percussion schuetzen rifle, which has a silver shield inlaid into the side of the buttstock which is engraved "C. SCHOETTLER MAKER PRINCETON ILLS".