[mtfeeney = Baron]

I saw posts by various people that mentioned it is obvious when you're possessed.  First, where does it say that in the books?  Second, is there any way to hide whatever it is that makes you look possessed?  A spell or disguise or something?

[Falconer]

Core Rule book... the rules for noticing magic.

Make a perception test with a threshold of 6 - force.   So anything force 5 and up is bloody obvious... force 4 pretty damn easy to notice.   And force 3 still reasonably easy to notice for one person... and highly likely that a crowd will (highest perception in the crowd +1 die for each additional).

[UmaroVI]

Street Magic 95 is actually the rule for Possession, specifically.

[Falconer]

Possession or Materialization doesn't matter... they both fall under the normal rules for noticing magic.

A spirit is always obviously magical as per those rules unless it has the 'realistic form' power.

Remember an earth spirit isn't necessarily a walking statue in the DnD fire elemental sense... it could be a fully clothed girl with long brown hair and eyes the color of stone.  (automatic powers are always on... so a fire spirit's elemental aura does tend to make them burn a bit and make that much obvious).

[mtfeeney = Baron]

I thought the rules for noticing magic was for noticing the casting of spells.  You're telling me that even a sustained spell is somehow noticeable?   That seems silly.  A sustained increase charisma spell would have the opposite of the desired effect.  You boost the charisma, but everyone knows you have magic boosting your charisma and distrusts you.

[mtfeeney = Baron]

It actually says very clearly that what is noticeable is the use of magic skills.  In the description, it also says they're setting a look of concentration or hand gestures and the like, with a possible shimmering thing if the force is high.  This wouldn't apply to someone affected by a sustained spell our possession.  The rules the other guy mentioned in street magic, though, describe possession perfectly.  Damn.  So I saw somewhere a mention of using a spell to hide the possession, any clues?

[Thrass]

As Umaro pointed out there a special rules in street magic that say spirits are obvious in their materialized form, even when resembling a toaster.
There is the realistic form power for spirits but I dodn't know if realistic form and possession can be combined.

Inhabitation is an exception to the rule, that spirits are (exception realistic form) always(!) obvious.

Umaro gave the rulebook and page number, without looking I'll direct you there too.

[UmaroVI]

Possession or Materialization doesn't matter... they both fall under the normal rules for noticing magic.

A spirit is always obviously magical as per those rules unless it has the 'realistic form' power.

Remember an earth spirit isn't necessarily a walking statue in the DnD fire elemental sense... it could be a fully clothed girl with long brown hair and eyes the color of stone.  (automatic powers are always on... so a fire spirit's elemental aura does tend to make them burn a bit and make that much obvious).

No, this is wrong.

Summoning the spirit falls under the normal rules. However, if you look on p95 of street magic, Materialized spirits are in fact always 100% obvious, no test needed.