Someone with Snapchat Plus can often be identified by a few key signs:

• They may have a star badge next to their username or profile picture, which indicates premium membership, though this badge can be hidden by the user.
• Their Snapchat app icon might be customized, differing from the regular ghost logo, which is exclusive to Snapchat Plus users.
• Their stories may remain visible for much longer than the usual 24 hours, sometimes up to 7 days.
• They can know how many times their story has been rewatched, which is a unique Snapchat Plus feature.
• They might pin friends to the top of their chat list, a feature not available to regular users.
• They could have access to Ghost Trails on Snap Map, showing where friends have recently been.
• Premium chat wallpapers or customization options for the app's appearance may also indicate Snapchat Plus usage.

To confirm, checking if the user has a star badge on their profile or next to their name in chat is the quickest way, but absence of the badge doesn't definitively mean they don't have it since users can hide it.