There are two hidden butterflies the the Fringe episode White Tulip, which are very similar to the butterfly glyph shown before commercials.
The first one can be found in Alistair Peck's kitchen while Peter looks through the photo album.
* Thanks to Spacegundam from the FringeTelevision twitter feed for finding this one!
A second butterfly can be found in Alistair Peck's lab, right as the FBI bust in to save Walter.
BTW, who is that dude in the photo?
This makes three hidden symbols in this episode so far, including the hidden seahorse. I feel like we've just hit the tip of the iceburg...