What does this margin symbol in the SSMS text editor mean?

While editing text in SSMS I mistakenly pressed a random keyboard combination, which I think began with Ctrl-K, and found this diagonal arrow symbol appeared in the text margin where the breakpoints normally go:

Can anyone tell me what it means?

SQL Server 2016 13.0.15900

I found the answer on Stack Overflow, as soon as I remembered that SSMS is a 'special flavour' of the Visual Studio Shell.

In short, it's a Task List item, which is toggled on/off with Ctrl-K, Ctrl-H. Items can be displayed with the menu View/Task List.

StackExchange Database Administrators Q#217897, answer score: 3