Near the end of Total Recall (2012), does the missing symbol on Quaid's arm symbolize that it is all a dream/fake memory? And, if so, why does he just accept it?
Here is a detailed comparison between the Theatrical and Extended Director's Cut. One of the differences is an additional scene at the end:
Doug looks down and removes the bandage from the spot where the injection tattoo was burned in at Rekall – it cannot be seen anymore.
One could interpret this as a hint that Quaid is still in a dream world. Although, that 'tattoo' might have been just a stamp mark that had rubbed off.
These set of dialogues has to be especially revised while he is being injected with the Chemicals from the chinese guy.
You could be working for the Resistance. Maybe you work for Cohaagen. Or why limit yourself? Why not both?
You're going to have such a good time, you're not going to want to come back. Look at that. Looks like your wife does have a man who appreciates her. No conflict there. Sorry. Still the best way to get chemicals into the human body.
Let's get this show on the road. Get ready to save the world. Happy trails, man.
And from there on he goes on exactly does that, saving the world.
Everything indicates that he is not dreaming, except for the symbol, but if it's all a dream Quaid´s should never would have dreamt about Melina before he goes to RECALL and that entire first scene doesn´t make sense.
Now assuming that is all real there is no explanation for the symbol. So in my opinion it has the ending wrong.
There is no reference that the symbol is permanent. it could be as simple as an ink stamp and can be erased easily, so imho everything is real or as you say the first scene would make absolutely no sense.
My theory is that Quaid never actually went to the Rekall lounge (where the Asian guy injected him). Cohaagen and his group just implanted that memory into him that he went there. So that's why he doesn't have a scar.