German umlauts often occur when a noun is plural or an agens noun is female, e.g. _Arzt_ '(male) physician', _Ärzte_ 'physicians' and _Ärztin_ 'female physician'. There are several cases where a short notation for both singular and plural or, more frequently, male and female singular are desired. A number of notations are commonly encountered, e.g. (not showing number pairs) _Doktor(in)_, _Doktor/-in_, _Doktor/in_, _DoktorIn_, _Doktor_in_, _Doktor*in_.
These only[^1] work well if there is no umlaut difference, i.e. neither _Ärzt/-in_ nor _Arzt/-in_ would be appropriate. A way to show the umlaut dots are conditional would be required but is not available in plain text systems and complicated to achieve in most rich text systems. Unicode has '⸚' HYPHEN WITH DIAERESIS (U+2E1A) to offer, i.e. _Arzt⸚in_ or _Arzt/⸚in_. This is also very uncommon, but may be used in some linguistic texts. I believe the most intuitive solution would be tiny parentheses before and after the two dots. This has no established usage as far as I am aware of, so would probably not qualify for encoding in the Unicode Standard. However, if it would qualify nevertheless, should this be a new atomic diacritic mark, e.g. COMBINING PARENTHESIZED DIAERESIS ABOVE, or two characters, e.g. COMBINING OPEN PARENTHESES ABOVE and COMBINING CLOSE PARENTHESES ABOVE to be used with COMBINING DIAERESIS (U+0308)? [^1] Yes, there are other cases where the stem changes in different ways, but that is irrelevant here.
