can someone tell me what this thing is?

[LSDMT]

55852

i can't click on it and don't know what it is or why it's there..

[Zacchaeus]

It is an indicator that if the PC does not have proficiency in the armour they are wearing that skill will be rolled at disadvantage.

See here https://fantasygroundsunity.atlassian.net/wiki/spaces/FGCP/pages/996641917/5E+Character+Sheet#Skills-Tab

[LSDMT]

Thank you!!