Translation site here:
https://www.portland.gov/transportation/walking-biking-transit-safety/play-loteria-go
"LoterĂa is a traditional Mexican game, similar to bingo, but using images on a deck of cards instead of balls with numbers. LoterĂa Go is a super-sized version of this that gets you outside and walking to neighborhood parks.
Can you find the LoterĂa cards we've hidden in the streets?"
Looks like it was something particularly targeting Spanish-speaking residents which makes sense. I'm sure some postcards didn't cost enough money to put a dent in any budgeting.