Thanks to all for your replies
Triangles seem to be typical of armored divisions.
@ Stephen C. Willoughby: I'd have to disagree, the 775th did indeed fight in the Pacific but was part of the first armored (the bigger part of the division was indeed sent to Europe). I can show you almost identical markings from both Italy and PTO if you're interested, in fact it's got me confused and I'm trying to work out where a particular marking was used (it's a blue triangle in a white circle without the tac mark to the upper right). Typical of the 1st armored division command, but also of the 775th.
Thanks and best regards
Cadre may have come from the First Armored Division and the similar tactical markings were used but the 775th appears nowhere on any TO&E of the First Armored Division. Similar markings in no way implies organizational affiliation.
It was a separate independent battalion under Army or corps command. In the Philippines they often operated with to the 37th Infantry Division.
Triangles are typical of armored formations because the bumper insignia of armor is a triangle which is from the tricolored armor triangle insignia.
And I have a comprehensive US Armored Division decal sheet that has all the 1st Armored, 6th and 20th tactical markings on it. I used it to build one of the 1st AD early M4 .ca. 1944.