there seems to be a numbered imprint on the back of this stamp under the gum. i'm not an expert on u.s. stamps but this does seem strange. stamp is a140 and type unknown and 1914-16 issues. anyone know about this and what type this might be. thanks
Can't address the cause for the numbers under the gum. Your image is a bit too small to be absolutely sure (would need a better look at the ribbons), but it looks to be either a Scott #455, if watermarked or #492, if not watermarked. To me, it has the look of a #492 rather than a #455. See stampsmarter.org for a good reference for typing the W/F series.
It is nearly impossible to tell much without having the stamp in-hand, however it appears that the digits are in reverse and very light, thus more likely a transfer from a secondary source after sale and thus also on the gum surface rather than under the gum.