Pattern staining on the face of a ceiling tile may be due to three causes:

1) Dirty water may have dripped onto the back of the tile and soaked through to the face causing discolored stains. These will normally be yellow or brown in color and probably due to ferric oxide (rust) contamination. Check for possible roof leak or pipe leak such as sprinkler, HVAC, supply and waste lines.

2) Tiles in the immediate vicinity of air grilles or diffusers sometimes display black marks or streaks. This is due to dirt in the air being deposited on the tile’s surface as the air emanates from or returns to the distribution system.

3) Heat from a room will rise (due to convection) and migrate through a suspended ceiling towards the (normally) cooler ceiling void. Minute particles of dirt in the atmosphere will also rise and be deposited on the ceiling tile’s surface.
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Pictured is a ceiling tile with water staining.