No problem! Some of the pictures are a bit obscure :P The one at the bottom of the S is Steve sketching Stark Tower, from a deleted scene (http://screenrant.com/avengers-deleted-scene-captain-america/) set at the beginning of the Avengers. The one at the bottom of the O is a quinjet.

(Edit: Hum, apparently they didn't finish the special effects, so instead of seeing Stark Tower in the background it shows the Metlife Building, which is there in real life, and Steve appears to be drawing something from his imagination :P I could have sworn I've seen a version with the Tower edited in, but I can't seem to find one now so I may be mis-remembering.)