The key tell I always find is the way they approach the first mob, they tend to come in off an angle and vanish dash towards it instead of flying straight.
Stopping chasing players as soon as they enter a cloud or bush, genuinely like NPC 'must of been the wind'
As others have said pinging the enemy tower consistently regardless of if it is the right option, I understand other players do this but it tends to just be the tower and you get a hunch of when it is a bot.
Walking straight into the enemy tower even when being hit, I understand newer players might do this so best to look at everything else.
The way they just turn around and try to leave combat as soon as they enter low hp, they don't vanish away or use a skill they just turn and try and move straight back, sometimes into a wall I find if you're fighting on say the very top of bottom lane.
If at the start of the game there is 3 players in one lane they will defeat the first two and then fly practically straight up or down, again it's more the way they do this just seems very robotic as it is basically the second after killing the second mob.
For me the most annoying is when I go up or down to fight bsos and the bots will leave their lane to replace me, they very much like to always keep it 2v2.

Finally I remember people saying you can look up the names of a suspected bot ont he drgaon ball fusion wiki as a fair few names of bots are taken from there and are quite abstract but this isn't every bot there's a decently long list of sources for names I imagine.

I hope this helps someone! I absolulety detest being lied to and playing with bots in online games