From 1994: STRONTIUM DOGS THE POSTER PROG issue 1, a one-shot spin-off from Tharg's Command Module.
Poster mags were quite a sideline for Tharg between 1993-95 with five dedicated to JUDGE DREDD and one apiece for SLAINE, ROGUE TROOPER, NEMESIS and the Dogs.
The format consisted of a giant poster with an original six page strip printed on the reverse.
The very first, albeit unofficial, 'Poster Prog' was published within months of 2000AD's launch making it one of the very first spin-offs. The DAN DARE POSTER MAGAZINE hit newsagents in August 1977, tucked into the schedule between the first 2000AD SUMMER SPECIAL (not yet the more familiar Sci-Fi Special) and the first 2000AD ANNUAL.