How to denote a number if # cannot be used? (What are alternatives to # symbol?) [closed]

I have data file containing titles like

Invoice #ZT-123456 June 2017

or

Agreement #1_ABCD Foo Services

but I need to put these titles into an app where character # is not allowed. (Edit: And U.S. customer will see what I wrote there.)

What is the best alternative writing when I cannot use #?

I was thinking about something like this:

Invoice Nr. ZT-123456

or

Invoice nr. ZT-123456

Maybe I could use number but replacing symbol with complete word does not seem appropriate to me in this context.

Solution 1:

The standard American English abbreviation for number is "No." (uppercase N, lowercase o, followed by a period). For example, Invoice No. 65967.

No., no. written abbreviation

number. room No.145

Source: Kernerman English Multilingual Dictionary © 2006-2013