This special seal tag was developed by Jiraiya so it can be used to suppress the Nine-Tails' influence over Naruto Uzumaki. By applying the seal to Naruto's forehead, the Nine-Tails' chakra and personality recede. Naruto is left fatigued afterwards due to his chakra being suppressed
The kanji written on the seal is 押 (ō), from the verb 押さえる (osaeru), meaning "to suppress" or "to restrain".
When it was introduced, it could be assumed that this sealing tag could be used on any jinchūriki to suppress their tailed beast's influence.