Clearly the whole point is that it won't mean anything, except to the very few lucky people who've been given the key. It's a cheap and very private way of sending simple messages to Your Man in Halifax. Nowadays one just emails; via encrypted channels, of course.
None of which stops the numbers stations from having a cult following, a bizarre style of their very own, and hoard of conspiracy theorists who stalk them.
Pulsars are relatively mundane in comparison. They're neutron stars: single atomic nuclei the size of small industrial cities; the remnants of dead stars that weren't quite large enough to form black holes; spinning spheres with surfaces moving at sizeable fractions of the speed of light; powerful radio beacons "chirping" so precisely they were originally labelled "LGM" for "Little Green Men"—which they aren't, of course.
So nothing to write home about, really.
Numbers station
A song of distant, static-abraded numbers
the mechanism unwinds—monotonic and discrete.
It had an edge once, but not now
so neat as the mind recalls it. There's a gap...
...around the days she faked, in faking lived
and now has left behind. Don't think about the boy
and forget the laughter pasted—crudely—between the mind
and the point, too far to guess, where a neutron star spun...
...down, the definitive direction: empires, cricket balls,
angels tumble from the blue, and in doing so
draw nearer. The man reached for her once; unknowing,
implored some sweaty comfort for the fall...
...to pass the time, she builds a short-wave radio
from wreckage in the tracking station.
She turns the dial to sample languages; shrapnel
of news and song; the soul of the pulsar chirps...
...for a moment, and a tiny, tinny voice chants:
two, seven, five
two, seven, five
zero, zero, zero.
She grabs the code pad...
...which isn't there.
Something has ended,
she doesn't know what—
those days are over.