This picture is of the big TriMet logo that's still mounted on the south end of the bus barns–that big building at the northeast corner of SE 17th Ave and Holgate Blvd. If you ever see a bus with the words "CENTER GARAGE" on it, this is where they're going:
The story the logo tells is pretty basic. It was redesigned a couple years back; the logo was effectively and successfully simplfied, and the arrowheads were removed, reflecting the observation that bus riders don't necessarily have downtown Portland as thier origin or destination.
This next photo is of an old logo I particularly love:
This is on the side of a workshop across the street from PGE's main base, which just so happens to be just north of TriMet's headquarters on SE 17th Avenue. This logo is just plain cool (and I used this photo as the reference for creating my own Adobe Illustrator version (illustrated here and seen for the first time in this post).
Keep an eye on your surroundings. Learn not just to look, but to see, and you'll sometimes be surprised what will come at you.