It's a selmer USA model 162, professional alto: these were made in elkhart and were produced in parallel with the selmer Paris series I . They are excellent saxes, incidentally the Bach / Selmer catalogue for the UK had these listed at £100 more than the selmer Paris . Some had extensive engraving over the back of the body.
I own the model immediately prior (the Omega) and the one just after (the AS110).
These are not common in Europe where selmer Paris had pretty much the monopoly for pro saxes, but they are quite sought after in the us as they are excellent but go for roughly 1/3 of a modern Paris horn.
Hope this helps,
M.