Definitive stamp perforated "OFICIAL" for use on external mail sent from government offices in Guatemala City. The date given here refers to the decree which necessitated these perfins, but in practice they were applied to stamps requisitioned from available stocks, so the actual issue date is approximate.
The perfin exists upright, inverted, reversed and reversed inverted. Sn and YT do not distinguish between these variants.
Forged perfins exist.