Alphabetic letters could mean anything, or be abbreviations of some functionality of the equipment. You would have to examine the drawing to assess whether the letters have any significance or are just references for identification. Sometimes, the 'cross in a circle' symbol is used to indicate the view of a certain section on a drawing. otherwise it is a new one on me, unless it is a badly drawn Greek Ø ö or . Certain symbols are used to represent specific characteristics, such as viscosity, wall friction and other properties, but I would not expect them to be used to represent forms of process equipment other than for identity purposes within a given project.

It seems obvious that you do not have recourse to the originators of the drawing but, unless the meaning of the references add to an understanding of the purpose of the parts concerned, it would not seem to matter. ■