That does not appear to be one of the ISO 4217 currency codes. The closest I found was Netherlands Antillean Guilder (ANG), which is in Numbers and can be chosen as a currency if the region is set to Curaçao using File->Advanced->Language & Region. It will appear in the cell as Naf when the region is Curaçao or as ANG if the region is later set to something else.
Change the region to Curaçao, format at least one cell as that currency. Once you have a cell that has that currency in it, you can set the region back to what it had been and that currency will remain on the list as long as at least one cell has a number in it that is using it.
Or, if you won't be using currency conversion or other functions that require it to be a "currency", you can create a custom number format that displays the number the way you want to see it. There is likely to be a florin unicode character you can use. I don't think you can get it to do "accounting style" where the currency symbol is aligned left and the number aligned right but you should be able to create a custom format other than that.