I'd learn the meanings verbatim for the theory test, but in the real world, rely on something else, frankly.
Just last week a mate of mine was returning to a controlled field when his battery died. Apparently his alternator had given up earlier but he had never seen the warning for that. By the time his electrics failed he was well into the CTR, about to get his joining instructions.
His cellphone was in a bag in the back. Theoretically his passenger could have gotten it out and he could use that to call someone. That would have taken him, perhaps, five minutes. While holding in a CTR with several aircraft following him on the same arrival route. Not a good idea.
Fortunately the tower was on the ball (the lack of not just radio, but transponder as well must've given them a clue) and gave him light signals. He was safely on the ground a minute later. No drama whatsoever.
In addition to that - have you ever tried making a phonecall from inside the noisy cabin of a GA aircraft?
Personally, I think light signals are still a very good idea, even in 2015. If you remember red = bad, green = good, then you're halfway there.