The names of the Tethered are colored red in the credits.
Before the movie begins there is an on-screen message that reads:
There are thousands of miles of tunnels beneath the continental United States...
Abandoned subway systems, unused service routes, and deserted mine shafts...
Many have no known purpose at all.
The sound of waves crashing on a beach are heard over the Universal logo at the beginning of the movie instead of the traditional fanfare.