durch is a preposition meaning "through" (by means of), or "through" (by the use of) - this looks like an imperative use as it's just one word with an exclamation point. Mitteilungen is plural for "information", which is a little strange. The noun is die Mitteilung, meaning "message", "notice", "post" "information". I couldn't find another definition in my dictionaries. Could be the artist's name maybe? What about both words together meaning that the rider in the artwork is getting the message through - as in a messenger in war bringing information back to the rear from the front line? Sounds plausable.
Von zwei Übeln wählt man besser das, was man schon kennt.
