The Alexandre brand saxophones were stencil horns that were popular during the 1920’s to the 1970’s.
They are usually lower-quality/student horns built by major manufacturers. I couldn’t find a whole lot on Alexandre in particular except it seems that they used multiple manufacturers over the years with the main ones being Keilwerth, Amati, and maybe SML. Some other sites suggest that there were other manufacturers as well but don’t specify. It sounds like Alexandre was one of the lowest-bidder type companies… “Hey we need 100 more tenor saxes… Which manufacturer will give us the lowest bid?”
I didn’t see anything as far as Alexandre-company specific serial number info on any of my usual saxophone websites. In general, it’s probably not a concert-level instrument, but a good repair guy that has seen alot of horns could probably peg which manufacturer it came from… meaning a Keilwerth manufactured Alexandre will look exactly like it’s corresponding Keilwerth counterpart of the same model.
And with any instrument; “it’s not the size of the boat, it’s the motion of the ocean.” If it sounds good and plays well, than it’s a good horn.
http://www.saxontheweb.net/ (you can search and post to their forums if you want to dig deeper)