How do I make on-screen markers for off-screen sprites?

I have been trying to do something like show in this image of apex legends. The two names on the bottom left and top right are off screen but it has markers for each teammate. I am trying to do this for enemies on a top down game.. any ideas?

Any help would be appreciated.

https://gamespot1.cbsistatic.com/uploads/original/1581/15811374/3495559-apex%20legends%20snipe.jpg

Simplified:

clamp(object.x, viewport left, viewport right)

clamp(object.y, viewport top, viewport bottom)

Thank you for your reply, newt! I had to play around a bit, turns out the keyword is "ViewportLeft(<layer index>)" and "ViewportRight(<layer index>)" etc. I really appreciate this!!