An approach to conveying the concept of "emperor" is to use a palm back
"C" hand moving from the upper non-dominant side of the chest to the dominant
side of the waist. This generic sign can be thought of as meaning "royalty." The
movement shows the royal "sash" upon which initialized versions of "royalty" are
based. For example: king, queen, and Christ. (The general "royalty" sign
is not the same sign as CHRIST. The two signs have different palm
orientations).
In a high-context situation (a situation in which it is obvious what you are
discussing) it is possible to simply sign "ROYALTY" and your audience will
understand that you are referring to "the emperor."
[context]+ROYALTY = emperor (or any other big fancy head of state)
If for some reason you "really, really" need to reduce any ambiguity whatsoever
about the sign for "emperor" sure, go ahead and use an "E" handshape on it.
It a similar vein you can use an "R" handshape on the ROYALTY sign to narrow the
sign down to specifically meaning "royalty." However don't get smug
since someone like me will ask you to show me how you would sign the sentence:
The regent was unused to his new royalty.
(A "regent" according to the Oxford dictionary, is a person appointed to
administer a country because the monarch is a minor or is absent or
incapacitated). My point here is that "context" is ALWAYS going to be
important when deciding how to sign something so don't just "initialize" a sign
as your first approach. Instead, think about the overall context and then choose
your signs to fit that context.
Notes: