I play on my laptop. They look like sideways oil barrels. I thought they were a part of the soccer event.
I also get them once a day, I think like 5 of them... mine also look like large blue oil barrels. They started right about the same time as the Aid All feature appeared, and I think, show up in the Incidents list, but just as a Blank space, not with a location.
At first, they were usually only Supplies, I think like 15K each. Now have branched out to include Troops, Goods, and also Coin. I am on PC only, and have never seen any ads attached to anything here.