How dastardly do I have to be to auto aggro Guards?

[Captain Skinny]

I was 2 stolen horses in and road patrol guards would come up and STOP RIGHT THERE CRIMINAL SCUM, and so were the guards at the Imperial City gates.
I usually play good boys, so I just need to know the rules from being criminal scum, because I don't want running from guards to screw everything up.

[Jangointhesky]

The guards in oblivion are comically aggressive, you could pick up a plate or apple that is not yours and they will come for you. Be wary of opening shop doors at night (they will be locked and force you into the lock-picking mini game) which can make guards aggressive as well. Don't steal and only attack people who attack first unless said otherwise in quest (Dark Brotherhood).

[WingedKagouti]

The guards will only bother you if you get a bounty. To get a bounty a crime has to be observed by a law-abiding citizen. Most named NPCs in and around cities and villages will be law-abiding, but there are exceptions.

[Captain Skinny]

So I have been seen committing horse theft, and am sitting on a 250 bounty. I have more than enough to pay it off, but ♥♥♥♥ the man.
Is having this bounty going to make the guards auto target me every time I see one?

[WingedKagouti]

Yes, as long as you have a bounty any guard who can see you will try to catch you.

[Yzal]

All Cyrodiil guards are part of a hive mind, so if someone saw you stealing a fork in Anvil every guard in the province knows instantly.

[Zagorith14]

Either don't commit crime or don't be observed by NPC's committing those crimes. If you aren't willing to pay 250 to remove the bounty then you'll just have to deal with guardsmen chasing you down constantly.