There is not a display setting for that but I think you could hide that column by css. Something like this should do it but I have not tested it:
.memberlist table #t2, .memberlist table td[headers=t2] {display, none}
The settings for those icons can be found in Web.config, you could copy the relevant settings into user.config and change them, however in a future release I will probably change that to use some display settings that can be controlled from theme.skin since they are currently global to all sites in an installation and it would be better to be able to control them on a site by site or per skin basis.
Hope that helps,
Joe