There are a lot of signs of computer cheating, for example:
a) The distribution of the time is very similar in all moves independently of the dificult of the position.
b) Hard perfectly calculate solutions vs obvious solutions to win. For example in a position with great avantatge of material a long combination to win material vs a simply liquidation combination that conclude in a endgame without counter.
c) Allow a lot of counter of the oponent in positions with advantatge but this counter is perfect controled by tactical means VS tendency to reduce counter and search for easy positions with advantatge.
d) Checkmates endgames with perfect numerous of moves vs checkmates endgames that uses common techniques to checkmate.
There are a lot of things but with one unique thing is impossible to arrive a conclusion that the opponent is cheating.
a) The distribution of the time is very similar in all moves independently of the dificult of the position.
b) Hard perfectly calculate solutions vs obvious solutions to win. For example in a position with great avantatge of material a long combination to win material vs a simply liquidation combination that conclude in a endgame without counter.
c) Allow a lot of counter of the oponent in positions with advantatge but this counter is perfect controled by tactical means VS tendency to reduce counter and search for easy positions with advantatge.
d) Checkmates endgames with perfect numerous of moves vs checkmates endgames that uses common techniques to checkmate.
There are a lot of things but with one unique thing is impossible to arrive a conclusion that the opponent is cheating.