Its not every day that I get to contribute to this thread, but:
City postman (about 1900)
Designer: Klaus Oberli
Engraver: Pierre Schopfer
Series:- Post Delivery
Mi:CH 1325ya, Sn:CH 789p, Yt:CH 1254a, Sg:CH 1112, AFA:CH 1311, Un:CH 1254, Zum:CH 741x
Issued on: 1986-09-09
Size: 25 x 30 mm
Perforation: comb 13¼ x 13
Printing: Offset lithography and Recess
Face value: 80 Ct. - Swiss centime
1987-07-15 issued fluorescent
To differentiate the phosphorescent stamps of this series from the fluorescent stamps use a low wave length UV light such as 254 nm. Place the stamps on a table in a completely dark room, shine the UV lamp on them and shut your eyes. Turn off the UV lamp and immediately open your eyes. The stamps that are glowing in the dark are the phosphorescent ones.
My 2x2 block came out of a CH Philatelic Office holiday greetings souvenir folder.