Because they have signal lights on them, one can see if information is still being transmitted or received.
(they; have; signal lights; L:on them) (information; received; ) (one; can see; if information is still being transmitted or received) Context(one can see,List([41, 52))):(information; is being transmitted; T:still)
one can see,List([41, 52))
they information one information
have received can see is being transmitted
signal lights L:on them
if information is still being transmitted or received
T:still