The Great Old One patron give the ability Create Thrall
At 14th level, you gain the ability to infect a humanoid’s mind with the alien magic of your patron. You can use your action to touch an incapacitated humanoid. That creature is then charmed by you until a remove curse spell is cast on it, the charmed condition is removed from it, or you use this feature again.
You can communicate telepathically with the charmed creature as long as the two of you are on the same plane of existence.
My question is simple: How can you detect this condition? Does a detect magic or true sight spell work? (The ability does not say it is magic, or even a spell). Any other method?