It is not often that I make so little progress with so many clues.
Q/ The stamp: does anyone know what St Martin did for Eschen?
Q/ The slogan: does anyone know anything about the 1969 air show in Vaduz?
Two local newspapers
http://www.volksblatt.li/ &
http://www.vaterland.li/ archives did not help, Google got me nowhere ...
... but the slogan LUFT UND RAUMFAHRT AUSTELLUNG {AEROSPACE EXHIBITION} VADUZ 25.7-17.8.1969 seems clear enough, does it not?
TIA, Cheers,
/s/ ikeyPikey

Liechtenstein
Patrons of the eleven municipalities of the Principality (St Martin Eschen)
Catalog codes:
Michel LI 490
Yvert et Tellier LI 439
Zumstein LI 426
Stamp Number LI 435
Stanley Gibbons LI 482
AFA number LI 493
Issued on: 1968-04-25
Perforation: comb 11¾
Face value: 60 Ct. - Swiss centime
Print run: 1,462,006
Designer: Georg Malin