ŋ is carefully used for Pali by PTS in works comparing different languages, like in their dictionary, to avoid confusion with the Sanskrit m-dot letter. It's actually a very common character, U+014B, having not really a serious Uppercase. The Problem is that the character causes easy confusion with
ṅ, the fifth letter, last of the first row
ṁ deprives from the "Latin Extended Additional", U+1E41 upper case U+1E40 (certain browsers do not support it, my Person does not see it in Chrome- Android, for example)
ṃ U+1E43, upper case U+1E40. Even near the above most browser and scripts support it.
Reading a little, the modern use of dot-under is seemingly a ISTA-convention and not really originated in older traditions:
In the Devanagari script, anusvara is represented with a dot (bindu) above the letter (e.g. मं). In the International Alphabet of Sanskrit Transliteration (IAST), the corresponding symbol is ṃ (m with an underdot). Some transcriptions render notation of phonetic variants used in some Vedic shakhas with variant transcription (ṁ).
In writing Sanskrit, the anusvara is often used as an alternative representation of the nasal stop with the same place of articulation as the following plosive. For example, [əŋɡə] 'limb (of the body)' may be written with either a conjunct, अङ्ग aṅga, or with an anusvara, अंग aṃga. A variant of the anusvara, the anunāsika or 'candrabindu', was used more explicitly for nasalized vowels, as in अँश aṃśa for [ə̃ɕə] 'portion'.[7]
Underdot has actually a total different pronouncing:
In Inari Sami, an underdot denotes a half-long voiced consonant: đ̣, j̣, ḷ, ṃ, ṇ, ṇj, ŋ̣, ṛ, and ṿ. The underdot is used in dictionaries, textbooks, and linguistic publications only....
The underdot is also used in the Devanagari script, where it is called nukta.
ISTA:
The International Alphabet of Sanskrit Transliteration (IAST) is a transliteration scheme that allows the lossless romanization of Indic scripts as employed by Sanskrit and related Indic languages. It is based on a scheme that emerged during the nineteenth century from suggestions by Charles Trevelyan, William Jones, Monier Monier-Williams and other scholars, and formalised by the Transliteration Committee of the Geneva Oriental Congress, in September 1894.[1] IAST makes it possible for the reader to read the Indic text unambiguously, exactly as if it were in the original Indic script. It is this faithfulness to the original scripts that accounts for its continuing popularity amongst scholars.
As thought this usual deprives from Hindi, Brahmic, Mahayana and norther traditions, later, prefering also the "am" spelling rather then the in the Pali Tradition used "ang" spelling. Of which first usually is not understood in traditional countries when citing Pali.
It's a matter of nature that "on-householding"-traditions are most influent global.
Nobody, so serious it is, in the west, would understand when one says "Sangsara" instead of "Samsara". Thats a sample of the two worlds. The use of the Sanskrik m with dot below, simply puts into the decay of traditional Pali pronouncing. Who would think much only some years ago after change. In ten years, with the decay of citing traditions, with the missing of differences, it would be simply gone.
Best, since its used as a diacritic also in other traditional scripts, would be to follow here with a diacritic also in roman script, possible making use of the most used ring above as well.
Saំsar(a), Saំveg(a). Saំំgh(a) or Saṅgh(a)?
This is something my person would give the Venerables to consider wisely and it's never really of long term disadvantage to accept burdens and bear limited global acceptance.
It would be, as the occation seem proper to express, good if the Sangha and it's language would be given autonomous language recognition, incl. fonts, characters and unicode block. This matters actually many different scripts, and thinking on Khmer transliterations and ways in action, following "productivity" it destroys a lot and nobody will in 1 or two generation be able to trace origins any more.
Yet of course its something only those in worldly charge, if wise and attentive, could order and give, and not the result of "marxists" natural laws conducted by crowd work and flow.