Vitreous glance

[Magpie]

Chambers whirring, - no need for the comma
behind their eyes
as their's
trace mine. - the rest of the stanza reads awkwardly to me especially with the repetition of 'their', firstly we don't know who 'they' are. 

'behind passengers eyes
as they trace mine'  -- might work better. But I get the feeling that you are wanting to keep the big reveal to the last line?
It poses a problem of sorts.

Lights flickering,
features hard to define.
Separated by grate
and iron plate;
digging for a sign-  - I like this stanza, although unsure about 'digging' as a word choice, and also not sure what the dash is for at the end.

until swallowed, - 'swallowed' by the tunnel?
by a rumble and flicker, - would 'with' work better than 'by' -- repetition of flicker from above
down the subway line. - nice ending - I like the reveal

I enjoyed this poem, not so sure about the title and what it refers to, eyes? windows?

Cheers for the read
Mark