I am not a number!

We spotted this Asian-looking women wandering around next to Loch Katrine today.  She was carrying a large inflatable No.5 wherever she went.  Can you guess why?

Note to the bear - she had a genuine instamatic camera with her.  This confused me as I understood from my assiduous attention to NHK World's Great Gear series that these are incredibly popular in Asia - but she had a broad Glasgow accent...  are they a thing out west now?