The standard signature processing depends on the version of Notes/Domino installed. Prior to release 8.5 you could have two local signatures, either a simple text based signature stored in the calendar profile or an HTML file stored locally on the workstation.
In 8.5.1 this was changed to two possibilities either a text based as before but then a Rich text based signature that was also stored in the calendar profile.
In 8.5.2 the old possibility of an HTML based signature was added back in by IBM. So in 8.5.2 you have 3 choices; either a simple text based, a rich text or an html. The first two are stored in the persons profile document within the mail file. The html file is still stored on the workstation.