What does this red icon mean?

@Peru Bob 

Just click and drag the CTI and go over a timeline marker or even the in/out points (timeline markers).

That little dude shows as long as the mouse is still clicked. Also, it shows only when the snapping magnet is on, so I think it's just an indicator that you're over the marker or in/out points.

I notice we are talking to ourselves here... no sign of the OP yet. Not sure how he got red, maybe he colored it for easy identification? 

Despite the lack of support here! 😉  I can make it happen in Green. So, I'm pretty sure it's not the prefs and not a glitch.

I agree with MarekMularczyk . 

Try resetting the preferences:
https://community.adobe.com/t5/premiere-pro/faq-how-to-reset-trash-preferences-in-premiere-pro/td-p/8236158?page=1

If that doesn't work, try resetting the Workspaces:
Reset a workspace
Reset the current workspace to return to its original, saved layout of panels.
1. Do one of the following:
• Click the Workspace menu icon and select Reset to Saved Layout.
• Choose Window > Workspace > Reset to Saved Layout.
from here:
https://helpx.adobe.com/premiere-pro/using/workspaces.html

If that doesn’t work, try updating or rolling back your graphics driver directly from the video card manufacturer’s site. If NVIDIA, do a clean installation of the latest Studio Driver (NOT the Game Driver).

If that doesn't work, try creating a new project and import the old one into it.

It looks like a glitch to me because it looks like two playheads together (two blue lines)...

I believe that notes a timeline marker.