Tapping a user from a specific site view in the iOS app will take you to their network profile, with the originating site selected as the top account. If the user is a moderator on the originating site, their name will be displayed with a diamond:
However, if you access the same user's profile from a site where they are not a moderator, the diamond will disappear. While this in some ways technically makes sense, having the diamond displayed in the "network profile" view being dependent on whichever account happens to show up on top seems more confusing than anything else, especially given that moderator diamonds are not displayed next to the account itself.
Ignoring the fact that it may make more sense to go to the site-specific profile in the first place, moderator diamonds should be displayed consistently next to the user name in network profile, and should be displayed next to the site name in the accounts list.