I like Color Me Katie‘s ways of thinking!
She’s done multiple variations of Doing Something Small And Unexpected For Strangers. (She also does Improv Everywhere. I’m convinced she eats random acts of kindness for breakfast.)
1) Rummage around for a pile of small rocks and stones.
2) Paint them.
3) Paint hearts on them. (Prefer pumpkins? Set on snowpeople? Favor 4-leaf clovers? Any of your gentle boatfloating symbols will do.)
4) Take them back outside and leave them for others to find.
[Color Me Katie: Scoot scoot to check out more of her ideas!]