Blue line under nickname-what is it?

[ampere]

What dictates whether your nickname has a blue line underneath it or not? That others can click on to look at your history. Mine does but I want to de-line it!

TIA

Hang on- mine's disappeared! I'd made my profile 'private' but the next post I made was still underlined- or was it??!

make your profile private

yours isn't clickable btw