With the onset of weak two bids, some ambiguity has been uncomfortably introduced regarding the meaning of an overcall at the two level. Following a 1S bid from the enemy, does 2H show 13 points and 5 hearts? 7 points and 6 hearts? Maybe 10 points and 4 hearts? Ambiguity has its inevitable place in bidding, but this is not a good place for it.
I propose that we standardize on the popular system of weak jump overcalls, though it might feel unintuitive at first.
A jumping overcall is the equivalent of a preemptive weak-two opening bid, showing say 7-11 points and a six-card suit; in the case of the overcall, though, the suit ought to be quite solid, without more than one missing honor.
A nonjumping overcall at the one level shows 10 points and a five-card suit (unless Bryan is the bidder; Bryan likes 13-point overcalls only.) A 1NT overcall shows standard 1NT opening, with the addition of a stopper in the enemies' suit. A nonjumping overcall at the two-level is strong, showing opening points and a good suit, except as spelled out below.
If you have a mammoth 18+-point hand, just double and bid your suit next round.
The quirk to remember
If you would have to jump to the three level -- e.g., opener bids 1H and you have six good diamonds and a weak hand -- don't jump, except to show seven cards. Your nonjumping overcall is thus either strong or weak, which will be clarified by your rebid.
Responder should bid if she has 10 points or good trump support. Raise partner in his suit to invite to game. A new suit is forcing for one round. NT is limiting, around 10 points and a stopper in opponents' suit.
When the bidding comes back around to you, the overcaller, pass or return to your suit cheaply if your initial overcall was weak. Any other bid implies that it was strong and forces to game.