How do I know if someone watched my Polo?

When you open a conversation, you'll see the Polo timeline along the bottom. This displays all of the Polos you've sent and received. Newer Polos will be on the right side. 

You'll know if someone has watched the most recent Polo if there’s a small circle icon with their profile photo in the lower-left corner.

You can also tap and hold the thumbnail of a Polo. At the top of the pop-up menu, you’ll see Watched by, along with the names of the people who’ve viewed it.