The stamp is SG 1063, from 1958 (8 Oct). Issued to commemorate 400 years of Polish postal system. Cat val is the minimum. It's in a series of 5 (from 40 g to 3 zloty 40); there was also a 2 zl 50 in a similar design issued on 24 Feb.
There was a good stamp (printed on silk) issued in 2008 to celebrate the 450th anniv of the postal service:
Posted 12/20/2010 10:09 am
