What key symbols indicate that a cylinder is cross keyed?

In a master key system, all keys and cylinders have key symbols.  These key symbols clarify where the cylinder fits into the master key hierarchy and what keys will operate it.  A cross keyed cylinder is a cylinder that has multiple change keys operating it - instead of just one.  

In DHI Nomenclature, cross keyed cylinders have a symbol that begins with an X.  Non-cross keyed cylinders are not permitted to begin with an X as this clearly denotes cross keying.  

The two types of cross keyed symbols are as follows:

• X1X, X23X, X47X, (any number between two x's.)  This style does not have a unique operating key.  Rather it is operated only by keys from other cylinders.  Applications for this type of cross keyed cylinder include: the front door to an apartment that all the residents get into or the common room shared by 2 or more dorm rooms.  
• XAA1, XGGM2, XB11, XAC3, (any key symbol preceded by an x.)  This style does have its own unique operating key.  For example, XAA1 is operated by key AA1 in addition to any other key that is specified in the operating note.  An application for this type of cross keyed cylinder include: An outer office door that is operated by an admin assistant as well as the occupant of the inner office.