A sarcasm tag indicates the poster is aware that a statement such as: “Indians, blacks or anyone other than white are incapable of being racist.” is absurd and ridiculous.
What does the sarcasm tag look like or do you just say sarcasm?
A sarcasm tag indicates that the poster knows that at least half of the people reading the post are to damned ignorant and/or humorless to recognize sarcasm when they see it.
Often, they are the same ones who can not link/differentiate subject and direct object (let alone an indirect object) in a clearly written sentence.