Here are some distinctive styles of “POST CARD”. Otherwise, try my Publishers’ Initials Logos and Series page.
Blum & Degen

Golike & Wilburg

Knackstedt & Näther
K&N produced cards for a number of Scandinavian publishers in a distinctive font and wording.
Source: Famgus Vykort
Lichtenstern & Hariri

PB, Harlesden, London N.W.

Valentine & Sons

Wyndham & Company

Lawrence of Dublin used the same design albeit sometimes in green.