It is only visible on their profile pages.
Two examples:
Lukmat was vinku before.
Cloutsy was SMMnet before.
Both have posted in this thread:
https://www.blackhatworld.com/seo/should-i-report-pm-dick-or-just-ignore.1376800/
However, I don't see any icon against their names in that thread as seen below.
Lukmat's post:
View attachment 195909
Cloutsy's post:
View attachment 195910
However, if I go to their profile pages:
https://www.blackhatworld.com/members/lukmat.6100/https://www.blackhatworld.com/members/cloutsy.1225369/
The icons are indeed available against their names as seen below.
Lukmat's profile page:
View attachment 195911
Cloutsy's profile page:
View attachment 195912
When I click on those icons, I can see that they were vinku and SMMnet.
Lukmat was vinku:
View attachment 195913
Cloutsy was SMMnet:
View attachment 195914
These two members do not have anything to hide and hence have not restricted access to their profile pages.
However, one can hide the profile page if so desired. In that case, there needs to be a way to know the member's history.