Hi Effjaelle,
I'm Ahmed and I am here & happy to help.
Is this still there? If yes, he can hover over there and see what it is as it's the first time to see this icon and I have done a lot of reproducing of this and a lot of research and unfortunately, I did not find anything related to this. It could be a system glitch or something like that. As I have also locked channels a never have seen this icon.
I hope this helps! Let me know if you have any further questions or concerns.
Best regards,