A 98 contention:
Quoth E’Tallitnics:

A98: To spot something that is hidden make a contested skill check: your Wisdom (Perception) vs its Dexterity (Stealth). In a tie nothing changes, which means that the Stealth didn’t work, since they were noticeable before the attempt.
If the guard was not aware of the rogue before, then on a tie (where nothing changes), he would remain unaware of the rogue. The check should be rolled at the point when the rogue could have become noticeable, and so, before the check, the rogue was not noticeable.