What does the inital /dⁿ/ stand for? While answering @Qiangong2's question here: Are Characters customized in different provinces due to dialectal differences? I was looking through the table on 四川方言字.
On the table the following initial keeps showing up:

/dⁿ/

For instance here is one single entry:

 | nang¹ | dⁿaŋ˥ | 形 | 瘦小、弱小

The entry for this word in《成都话方言词典》is notated as:

 [Ĩaŋ⁵⁵] 身体瘦小

《现代汉语方言音库 • 成都话音档》writes it as:

 naŋ⁵⁵ 瘦小

I've seen both /n/ and /Ĩ/ as an initial, I have a preference of the two, but I have never come across /dⁿ/. I'm guessing that a simplified writing of /dⁿ/ would be: d‘, but how d‘ sounds anything like /n/ or /Ĩ/ is beyond me.
Ideas?
It's the IPA diacritic for the nasal release from a stopped consonant:
Quoting right from that Wikipedia page:

That is, the /d/ is released directly into the /n/: [ˈsʌdⁿn̩].

Where [ˈsʌdⁿn̩] is the IPA transcription of the English word &quot;sudden&quot;, where the blocked air flow from the articulation of /d/ is released through the nose (you should feel it vibrating in your pharynx).
For those who don't have the font installed, I believe the character in the OP is: