Those are used a bit differently. You don’t put them right up to your eye; you hold it out in front. They’re mirrored on both sides, and you look through the hole at the target, but also look at the reflection of the ground in the back mirror-surface. When you can see the target through the hole, and can also see the reflection of the thing’s shadow (with a bright spot in the middle of it), you’re aimed right.
Thanks to @CalMeacham for introducing me to how such devices work.
I understand, but note that at least some emergency mirrors come with instructions to and are set up to hold them close to the eye: look at the first guy here: How to use a Signal Mirror - Outdoor Revival
His mirror appears to be of the type with a small reflector around the hole, instead of the entire back being silvered.
The first picture shows that, but the page also says that it’s important to use them right, and the directions don’t actually match the first picture (rather, they seem to be the same method I described).
I don’t remember a doctor ever using them. But I also don’t remember a portrayal of a doctor using them. Maybe they were representative of doctors in 30s movies, but not anything more recent.
Do people have any examples of recent uses in movies or TV? Even comical ones?
Should have searched first. “Hand mirror” reveals that Cecil (anybody remember him?) did a column on this back in 1993 and the topic of what the heck are these popped up several times in the early years of the column. No one I found gave any examples of actually seeing a head mirror in anything, just wondering what they were.
The guy who played the hick doctor on Hee Haw wore one, as I recall.
Hee Haw ran from 1969 to 1997, so that doesn’t necessarily narrow down to recent.
Yeah, Hee Haw was simultaneous with Laugh-In. Prius vs. Pickup even then.
I learned to use one when I was an intern (1973-4). We had headlights but the head of ENT insisted we also learn to use the mirrors. As Qadgop said, they take a little getting used to. But once you figured it out, they provided great illumination of throats.
My dermatologist has been using one for as long as I’ve known him, 15 years. My husband first went to him 40 years ago and has a Monday appointment with him; I’ll ask him if he was using one back then and if he’s still using it now.
The text on the page is rather unfortunately written, since at least two or three different types of heliographs are pictured. The actual directions for the first one should be something like this:
The difference to a doctor’s mirror is that with the patient right in front of you rather than off towards the horizon, there is no need for the retroreflective thingy in the center to aim the spot of light. Also, a doctor’s mirror may be curved instead of flat.
Well, it was more recent than the 30s, the frame of reference you provided. Some gratitude. 
Didn’t remember anything, but when I was searching for images I found Dr. Mario from the 1990 game.
I can’t remember, did any of the doctors on M*A*S*H wear one?
Found one picture:
When I was a kid the family dentist used one. Weird looking bald guy. Wore a white jacket with the collar that closed around his neck. Im sure he was a sadist and tried to make himself look like a mad scientist to increase his pleasure by instilling fear in his victims.
Did he drive a motorcycle and sing a lot?
This cartoon popped up on my feed today. The image of a doctor wearing these things is still very much alive in the public consciousness. Here a recent cartoon depicts a doctor wearing one.
The last doctors I saw wearing them was Dr. Howard, Dr. Fine, Dr. Howard 
Blasphemy! Of course we remember the Perfect Master. Stone the unbeliever!
The mirrors may be decades obsolete, but you still see them used in graphics as a symbol for a doctor or the medical profession. It’s similar to the way an article about the Federal budget might be accompanied by a pie chart superimposed on the image of a Morgan silver dollar.
I doubt The Lockhorns are that currenr with the social gestalt