Here are some distinctive styles of “POST CARD”. Otherwise, try my Publishers’ Initials Logos and Series page.
Carlo Bassani
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.
Trenkler
Valentine & Sons
Wyndham & Company
Lawrence of Dublin used the same design albeit sometimes in green.
Langsdorf
Undivided-back Postcards 