Cancel that, I finally figured it out.
Au Spectre Solaire, 18, quai de l'Ecole et 38, rue Neuve Vivienne, Colcomb-Bourgeois
This is not a shipping stamp, but the maker of the paint colors. The stamp dates the painting to somewhere between 1849 and 1856, and makes it very likely French or German in origin.
This portrait is quite lovely, and would be even more so with proper cleaning and varnish removal--it's very, very darkened. Once the darkened varnish is removed, the signature can be read.
Given the quality, I feel there is a fair chance this is by a known artist. Unfortunately, given that photo, there is no way to tell.
If the artist is entirely unknown, the value in this condition would be perhaps $1,000.00. However, given the quality and the degree of darkening, that's a big unknown.