Within Visio there are several data types and you can format data based on several Format codes.

Fixed List, Variable List amd Boolean do not have special Format codes. (or do they?)
The Formats for the various Data Types are:
With a little exploring I came up with the following table of data format codes.
string | Normal | @ |
string | Uppercase | @+ |
string | Lowercase | @- |
Number | General | #.#### |
Number | General Units | #.#### u |
Number | Whole Number (3) | 0 |
Number | Whole Number with units (3 cm.) | 0 u |
Number | Floating Point (2.75) | 0.00 |
Number | Floating Point with units (2.75 cm.) | 0.00 u |
Number | Fraction (2 3/4) | # ##/## |
Number | Fraction with units (2 3/4 cm.) | # ##/## u |
Duration | Weeks | [w] ‘ew.’ |
Duration | Days | [d] ‘ed.’ |
Duration | Hours | [h] ‘eh.’ |
Duration | Minutes | [m] ’em.’ |
Duration | Seconds | [s] ‘es.’ |
Duration | Hours and minutes (1:23) | [h]:[mm] |
Duration | Minutes and seconds (0:12) | [m]:[ss] |
Currency | System Settings | @ |
Currency | $3 | U0 |
Currency | $2.75 | U0.00 |
Currency | 2.75$ | 0.00U |
Currency | $ 2.75 | U 0.00 |
Currency | 2.75 $ | 0.00 U |
Currency | 2.75 Unitef States Dollar | 0.00 UU |
Currency | 2.75 USD | 0.00 UUU |
Date | 10/3/1993 | {{M/d/yyyy}} |
Date | Sunday, October 3, 1993 | {{dddd, MMMM d, yyyy}} |
Date | October 3, 1993 | {{MMMM d, yyyy}} |
Date | 10/3/93 | {{M/d/yy}} |
Date | 1993-10-03 | {{yyyy-MM-dd}} |
Date | 3-Oct-93 | {{d-MMM-yy}} |
Date | 10.3.1993 | {{M.d.yyyy}} |
Date | Oct. 3, 93 | {{MMM. d, yy}} |
Date | 3 October 1993 | {{d MMMM yyyy}} |
Date | October 93 | {{MMMM yy}} |
Date | Oct-93 | {{MMM-yy}} |
Date | 10/3/1993 5:00 PM | {{M/d/yyyy h:mm am/pm}} |
Date | 10/3/1993 5:00:00 PM | {{M/d/yyyy h:mm:ss am/pm}} |
Date | 5:00 PM | {{h:mm am/pm}} |
Date | 5:00:00 PM | {{h:mm:ss am/pm}} |
Date | 17:00 | {{HH:mm}} |
Date | 17:00:00 | {{HH:mm:ss}} |
(Oct 1993 was just before the release of Visio 3)
The official Visio webpage describing the Format codes is here.
About Format Pictures | Microsoft Docs
( There is a note on that page mentioning predefined Formats. A list of those numbers appears to be here. https://docs.microsoft.com/en-us/office/vba/api/visio.visfieldformats )
As you may notice, that list is bit more extensive and I am in the process of making a webpage of a more complete set of examples. It is still early days and the webpage needs work. (I have yet to master table widths in WordPress. 😉 )
The webpage is Word Formats but it needs work. Eventually I will have a download on my download page that includes an Excel file of a more fuller list of Formats and a Visio document that includes examples (User cells) of how to use the codes, both the codes and the results. I will also expand the codes listed in the notes.
John… Visio MVP in x-aisle
JohnVisioMVP.ca