Joe Patrick writes
My son bought a Priv Day Travelcard from Baker Street Tube station this
morning and it had 4 yellow arrows at the bottom? Could someone please
tell me what this means, or are all tickets being issued like thi

Different coloured arrows for different areas of London.

Red in the north (on the northern end of the Piccadilly line at least);
yellow in the centre. I'm sure someone else will tell you the colours
used elsewhere.

Purpose? An easy way to spot people who have crossed Z1 'illegally', I
guess.

--
Dave