A string mute is almost always notated with an x. Several x's in a row, on adjacent strings, is used to notate a rake.
Right hand tapping (for right handed guitarists) is generally notated in tab via a t, in conjunction with the pull off and hammer on techniques used when executing right handed tapping. Thus, 2h5t12p5p2 represents traditional tapping technique.
When notating the tab for harmonics, the <> symbols are usually used, surrounding the fret which the harmonic is played at.