There is no publicly visible indicator to determine whether you have a profile on stackexchange.com - the usual options that staff can look at to quickly determine whether it's a real profile or a generated profile are only visible while logged in. And well, the act of logging in there automatically creates the profile so a user wouldn't be able to check their own profile without... creating the profile and thus rendering the activity moot (there's no confirmation of wanting to create the profile there, it just gets created when you first login).
So, in practice, it's not possible for you to know if you don't remember whether you've ever logged in there. That is why we advise users deleting their profiles to wait 24 hours to see if it disappears. If it doesn't, then they likely have a profile there. Though, because stackexchange.com doesn't confirm creating a new profile, we've had plenty of instances of users trying to login there to verify it's really deleted, and get stuck in a cycle of constantly recreating the profile. But that's another fun tangent.
