How do you punctuate the abbreviation of a hyphenated middle name (Charles-Moore) on a plaque? Some thoughts include: C-M ; C - M ; C.-M. ; C. - M.
I can't find a rule for this in the New Oxford Style Manual (2012), although the book gives the following rules for initials:
Initials before a surname are separated by full points, with a space after each:
J. S. Bach - E. H. Shepard - Hunter S. Thompson
although some modern designs, particualrly those of newspapers, omit the full points and spaces:
MR James - PJ Harvey - George W Bush
Normally, names given entirely in initials have points but no spaces (J.A.S., E.H.S., J.R.R.T.). When people are commonly known by their free-standing initials, these forms have neither points nor spaces (FRD, LBJ).
The general approach is supported by Rabinowitz and Vogel (The Manual of Scientific Style).
The Chicago Manual of Style (16th Ed, 2010) states that:
If two or more initials are used as an abbreviation for an entire name, no periods are needed.
Kennedy and Johnson soon became known as JFK and LBJ.
The compilers go on to state clearly:
Initials standing for a hyphenated given name should also be hyphenated.
Jean Paul Sartre; J.-P. Sartre; Sartre
However, this applies specifically to French names used in a US-English context, and they go on to say:
Since there is considerable variation in French usage, the guidelines and examples above merely represent the most common forms.
If cultural differences in approach are significant factors in making a choice, and linking orthography to common usage isn't sufficient to allow a sensible decision to be made, I would suggest looking at examples of usage in context.
For instance, the Wellcome Library abbreviates Kraft-Ebbing to KE. This would seem to be archiving shorthand;
and the Austrian Biographical Encyclopedia (Österreichische Biographische Lexikon 1815-1950) abbreviates Kraft-Ebbing to K.-E. which is the most formal version of the three. Given the intended use, assuming maximum formality, I would personally go with C.-M..