OK first I would have RAISED on the SB.. 5 6o is a crap hand.. what would you actually need to see on the flop for it to be a decent hand?
55x 66x 23 34 24 47 78 79... (89 makes a definite straight possibility for others)
So a raise from the SB is needed to
1. thin the field
2. make your c-bet on the flop make sense, if you don't hit, i.e. help with a bluff.
3. make post flop decisions easier.
But OK you have trip 6's. Without the raise pref lop there could be all kinds of hands out there. The raise should have raised the starting hands such that your worries would be gone on a flop like that.
Your biggest worry here is not someone having a 6 with a bigger kicker.. Its the likely hood of mid pairs hanging around and the size of the field. On a flop like that with no pref lop aggression mid pairs are likely to hang around as they will have flopped 2 pair and may well believe they have the best hand.
Therefore they will stay in the pot and may spike trips to their pocket pair giving them a full house.. and one that dominates your possible draw to a FH.
But saying that, its a flop which is unlikely to have hit anyone..
Bet out c-bet size (3/4 pot) and if someone raises, re-raise.
I would not call here for 2 reasons
1. They will most likely think you are bluffing
and further re-raise you on the turn by floating the flop and then re-raising you again on the turn to bluff you. ESPECIALLY if a scare card shows
2. I would not want to show 5 6 o down on a showdown.. even if it were the winner.. It would hurt my table image, so yes i would win the pot but give others the incentive to bet into me as I have shown I am happy to limp with nothing.
3. To me the biggest scare cards would be 7 8 9 or T because its those kinds of pairs that are well worth seeing a flop but not necessarily raising.
I would just be far happier with the hand had you raised pre-flop.. or folded