Navigation system

Can anyone tell me what the letter preceding the place name indicates on the 2002 E46 navigation system? When I have the split screen option in use there
is a readout of the current position. If I am travelling through the town of Stirton for example it might say S-Stirton. Sometimes I also notice the prefix L or U used also. I can't find anything in the handbook for the system which explains what this means.
Thanks David
Add pictures here
<% if( /^image/.test(type) ){ %>
<% } %>
Add image file
Upload is a website by car enthusiasts for car enthusiasts. It is not affiliated with any of the car or spare part manufacturers or car dealers discussed here. All logos and trade names are the property of their respective owners.