Some sannyasis go naked, and sometimes they wear red garments and pass under the name of kapalika. These are simply symbolic representations of their sinful activities
SB Canto 4
In this way, King Indra, in order to steal the horse from King Pṛthu's sacrifice, adopted several orders of sannyāsa. Some sannyāsīs go naked, and sometimes they wear red garments and pass under the name of kāpālika. These are simply symbolic representations of their sinful activities. These so-called sannyāsīs are very much appreciated by sinful men because they are all godless atheists and very expert in putting forward arguments and reasons to support their case. We must know, however, that they are only passing as adherents of religion and are not so in fact. Unfortunately, bewildered persons accept them as religious, and being attracted to them, they spoil their life.
As stated in Śrīmad-Bhāgavatam, men in this age of Kali are short-lived, devoid of spiritual knowledge, and susceptible to accept false religious systems due to their unfortunate condition. Thus they always remain mentally disturbed. The Vedic śāstras practically prohibit the adoption of sannyāsa in the age of Kali because less intelligent men may accept the sannyāsa order for cheating purposes. Actually the only religion is the religion of surrender unto the Supreme Personality of Godhead. We must serve the Lord in Kṛṣṇa consciousness. All other systems of sannyāsa and religion are actually not bona fide. In this age they are simply passing for religious systems. This is most regrettable.