The icon in this seal is a horizontal herm (a Greek signpost) with an inscription that reads, "Rhodouos".  A very similar seal was published by Virginia Grace in her landmark work, "The Stamped Amphora Handles Found in the American Excavations in the Athenian Agora 1931-1932" (1934; seal #62, excavation ID# SS-352 [SigmaTau]).  The differences are that the icons are mirrored, & the spelling might be slightly different, as hers was faint on the right side.  (See also seal #61, which is aniconic, but preserves the final Stigma; & although her text reads "Rho[do]uos", the last 3 letters on the seal are clearly "NOS".  The readings on all 3 of these specimens merit further research, since this one clearly appears to terminate with an Epsilon rather than a Stigma.)

The size of this seal is 1.8" x 0.6" (46 x 16 mm).

The photo above shows the overall jar side illuminated from above for the correct coloring; the light source in the photo below was positioned obliquely to highlight the potter's marks.