unidentified icon on menu bar
I have an unidentified icon on my menu bar. It does not exist in my applications. It's possible it's left over from something previously downloaded and deleted but I'm not sure. Every now and then it opens to a blank box. And if I click on it, a blank box shows up.
Can anyone tell me what this icon is and how I can get rid of it?
Here is a picture of it:
And this is what it looks like when you click on it:
Thank you for your help!
iMac, macOS Sierra (10.12.6)