On the other hand, R2 makes me think you're talking about Resistance 2, so it doesn't make much sense at all?!
Also - you're in a Titanfall 2 topic, so I don't think many people will be confused what game you're referencing if you use the acronym TF2.
You can never please everyone. During the beta test there were people complaining about the use of TF2. So folks started using R1 or R2 in the comments. I will just use TF2.