There is certainly nothing more we can do here.
2 seconds sound clip from Superman (1948) - Blast In The Depths (Chapter 12).
You can hear this line at 00:11:06.700 in the Blu-ray version of the episode.
Quote context
[...]
- This may prove that Lois was here, if it's hers.
- I wonder how this window got broken.
- Possibly in the struggle when Collier was shot, if there was a struggle.
- Maybe she's gone to the police station or the hospital or something.
- There is certainly nothing more we can do here.
- Wait a minute... This was scratched deliberately.
- A question mark and a cross.
- I don't know. But obviously, it was meant to convey a message to whoever might be here.
- A question mark. Interrogation mark. Cross. Cross.
- A mining engineer's guide. It may help me find a clue.
- Here's something. A list of mines and mining locations.
[...]