Two baffling London Underground signs – a dry dropper and a service void

Two baffling London Underground signs

Spotted on a recent trip on London’s tube network were these two curious signs.

I have no idea what a ‘dry dropper’ is, but it sounds like someone might suffer after a long cold.

Two baffling London Underground signs

I have to say that I was very curious as to what lay behind this panel. A portal into a different world, perhaps?