In general the clues that you are high elo are pretty basic.
-10 revives per game, and usually several garrisons
-Someone calls bot (instead of everybody just hoping they don't have to go)
-your queue times get high (10-20 minutes in blind, over an hour in draft)
-People in your games start trash-talking about cheesecake tier champs and OP spammers (kassadin/teemo, not jax/poppy).
-You start seeing the same bunch of people in your games over and over again.
-You start recognizing those players, chatting with them, and knowing what champions they usually play and which ones they are good with. Then you notice that several of them post on the forums a lot, and you recognize them there too.
-You start to recognize those same players are on the top 500 dominion players list on lolmatches
-You start to recognize those same players are on the top 100 dominion players list on lolmatches
-During the DD tournament on Saturday, you see those same people you know playing in the tournament
-During the semifinals and finals matches on DD you realize you recognize everybody who is playing.