Abbreviation of "number"

I'm personally not familiar with using "nr." but that doesn't mean it isn't ever done. His bib no. was 515 in the race would probably work, although you don't usually use abbreviations in normal prose. Save that for a chart. On the other hand, you can use the pound sign (#): He was #515 in the race.

Well, Anon, it depends on what you use as your style guide, doesn't it?

Abbreviations are a matter of style, not grammar, which means that there is no "always do" and "never do."  The most important thing for style is to be consistent within whichever style you choose to follow. You can use AP, or Chicago, or whatever you follow, including a house style.

The fact that you say "full stop" instead of "period" already tells me that you follow some different styles than I do.

I found two examples online in just moments that advocate for no. for number.

The number sign # (also known as hash) is mostly used for counting or ranking lists (ordinal numbering), especially in names and titles.
If the # is placed behind a number it's called a pound sign in the US (3# of sugar), if precedes the number it's called number sign, other countries use lb. for pound instead
UK, Canada, Australia, New Zealand, Russia and the rest of Europe use N°. If the superscript "o" isn't available then it's written as No. The abbreviation no. is also used.
In Germany the the Abbreviation Nr. for "Nummer" is commonly used.

Some information:

http://en.wikipedia.org/wiki/No.
http://en.wikipedia.org/wiki/Number_sign

In French, the dot depends on the last letter.  As the abbreviation of numéro (meaning number) ends with the last letter of the word numéro, we don't use the dot.  If the abbreviation was built with the starting letters like nu, in that case we should write "nu." (nu dot).

Another example is boulevard.  In English you write blvd but the rigth abbreviation is boul. in French. With the dot to follow the previous rule.

It doesn't apply to English. Even in French, I can't say if this rule is always true as in french, no rule always is.

Pierre