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.