To display in front of players, the two simplest ways I could think of: 1) take an index card. Fold in half lengthwise like a little tent. Cut two slots. Insert relevant markers:
|Deaf & Poisoned
2)Second option, just fold the marker in half and put a paper clip on it:
Downside is they might get shuffled around the table, upside is super simple, and your players can have tons in front of them.
I've seen Cyclopeatron use a little yellow slip with a lantern on it to indicate light bearer. I need to make some of those.
If you're using minis, Dan C. over at Dungeoneering Dad suggests the little color rings around milk and soda as easy to get, multi-colored markers.
What effects do you need? I'll try to make them.