The following results in combat are obvious without any dice rolling:
- Knocked back.
- Knocked down.
- Stunned; the heart attack mortal condition; and the agony, choking, daze, and ecstasy incapacitating conditions.
- Crippled.
- Hallucinating incapacitating condition.
- Retching incapacitating condition.
- Seizure incapacitating condition.
- Dead; unconscious; the coma mortal condition; and the paralysis, sleep, and unconsciousness incapacitating conditions.
However, it would require a Concentrate maneuver and a skill roll to distinguish between two conditions on the same line above in a fight (stunned vs. daze, dead vs. merely unconscious, etc.). Ditto to distinguish between two causes of the same condition (knocked down by failed HT roll vs. knocked down by failed DX roll, mental vs. physical stun, etc.). And ditto to identify
shock (the penalty due to injury),
irritating conditions (coughing/sneezing, drowsy, drunk, euphoria, nauseated, pain, or tipsy), or
wounds (missing 1 HP vs. missing 4 HP, etc.).
I would allow several skills to work here. Diagnosis is obvious, but other possibilities might be Body Language (to notice shock, tell types of stun apart, etc.), Physiology, Streetwise (to spot drunk, euphoria, etc., and to distinguish ecstasy/daze due to drugs from combat stun), and anything else the player convinced me made sense. For instance, I'd let a boxer make a Per-based Boxing roll to assess the results of his beating. The important part is the turn spent scrutinizing the target, not the skill. I'd probably give a bonus equal in size to the largest relevant penalty to notice irritating conditions and shock, too; drunk, with -4 to self-control rolls, would be +4 to spot, compared to +2 for tipsy. Likewise, -4 in shock would give +4.
However, the simple answer about stun is, "Yes, it's obvious when somebody is stunned." In general, if somebody wants to
fake still being stunned (or any other status above), the onus is on him to win a Quick Contest vs. observers' IQ or relevant skill.