From
https://www.cityam.com/mayor-of-london-election-sadiq-khan-pledges-to-name-london-overground-lines/

Sadiq Khan has pledged to give individual names to London Overground train
lines if re-elected as mayor of London next month.

Khan’s manifesto, released today, said the “London Overground network has
grown considerably over recent years” and that “to reflect this I’ll launch
a programme to name individual routes, giving each its own identity”.

The London Overground now has 112 stations over six different lines,
however none of the lines are named like on the London Underground.

The policy announcement will see a programme launched by Khan to choose
names for the six lines, if he wins re-election on 6 May, however no
details were given on what the criteria will be.