Published tablature in books and magazines usually have a curved line over or under the notes involved in the pull-off. Sometimes there is a “P” as well.
Pull-offs between two notes in internet tablature are represented by either a “p”, “^”, or both. The “^” is used for both hammer-ons and pull-offs, but you can tell the difference between a pull-off and a hammer-on by looking at the second note. If the 2nd note is lower than the 1st note, then it is a pull-off.
Similar to published tablature, standard notation uses an arc, but does not include the “P”.