SE Markdown appears to filter out
<nobr> tags, although browser support for this element seems to have been removed anyway.
The Unicode solution appears to be the "word joiner" character, inserted after the opening slash and before the closing slash.
Word Joiner. U+2060
word joiner behaves like U+00A0
no-break space in that it indicates the absence of line breaks; however, the
word joiner has no width. The function of the character is to indicate that line breaks are not allowed between the adjoining characters, except next to hard line breaks. For example, the word joiner can be inserted after the fourth character in the text “base+delta” to indicate that there should be no line break between the “e” and the “+”. The word joiner can be used to prevent line breaking with other characters that do not have nonbreaking variants, such as U+2009
thin space or U+2015
horizontal bar, by bracketing the character.
The character does appear to be supported by the font in use at EL&U, though I cannot speak for others used elsewhere on SE: /⁠A⁠B⁠C⁠D⁠E⁠F⁠G⁠H⁠I⁠K⁠L⁠M⁠N⁠O⁠P⁠Q⁠R⁠S⁠T⁠V⁠X⁠Y⁠Z⁠&⁠⁊⁠Ƿ⁠Þ⁠Ð⁠Æ⁠a⁠b⁠c⁠d⁠e⁠f⁠g⁠h⁠i⁠k⁠l⁠m⁠n⁠o⁠p⁠q⁠r⁠s⁠t⁠x⁠x⁠y⁠z⁠ƿ⁠þ⁠ð⁠æ⁠/
You can enter the character using the HTML entity
⁠, which seems to be to be the friendliest for both author and future editor. Entering the character directly and it will be unseen, to frustrate and to get deleted; entering the numerical entity is friendly for machines, but not humans who are not insufferable Unicode pedants.