This was a pleasant little hand-painted surprise I found across the street from the Oaks Park entrance. Samtrak was a small tourist railroad that ran between OMSI and SE Spokane Street near the Sellwood Bridge with this stop at Oaks Park. The train ran between 1993 and 2001. Here's more information about it.
Next time you go to Oaks Park, take a look to your right as you turn into the main entrance to the parking lot.