FWIW, beveled tone holes don't always mean Martin. Other manufacturers made saxes with soldered, beveled toneholes, like Couturier and York. With bell keys on the left, it probably is a Martin, though. To my knowledge, none of the other manufacturers continued making them into the 1930's when same-sided bell keys came on the scene.
I saw a "Chicagoan" alto many years ago on Ebay and thought it was a Martin stencil at the time.
Martin Handcrafts valuable? They might have "some" value depending on condition, but any Martin stencil alto in perfect playing condition probably isn't worth more than $500, and not much more than $300 for unfamiliar names. That's my 2-cents, anyway.
The exception might be the Dick Stabile stencil which has more features found on Martin's first and second line horns of the day.