Tac squad arm is the right arm of the mini. Most of them use it though. Some exceptions are the Blood Angels (blood drops instead), Dark Angels (arrow on side with point at either end), Black Templars (Chapter icon).
Ultramarines, Imperial Fists, Crimson Fists, Salamanders, White Scars, Blood Ravens all use it in varying colours.
I can't vouch for its accuracy, but this website shows a lot of the colours for the various chapters using tactical marines mostly as the model. The models are computer generated so most tend to have the same arrow up tactical sign whether they're supposed to or not.
http://www.philipsibbering.com/WH40KRP/40K_9_Marine_4_Chapters_1000.shtml