Two nouns in a row, or, is it OK to omit "de"?

Question

Two or more nouns are sometimes used consecutively, with the second modifying the first.

For instance, I recently received a mail whose subject was "Honorarios migración." This is, I suppose, shorthand for "Honorarios de migración" or, if we're feeling wordy, "Honorarios para el servicio de realizar trámites de migración".

Other examples: at a parking garage: "salida coches."; spam from an airline: "¡Venta fin de semana!"; signs in my colonia that read "venta garage."

Some of these usages maybe be due to space constraints, but that clearly isn't the whole story.

So, first, what is the name of this phenomenon?

Second, is this something you'd ever want to do in formal writing? If so, under what circumstances?

Answer 1

None of the cases you mentioned is gramatically correct; they should have used de.

As you suggested, it was removed to make it shorter, since it will be understood anyway.

Answer 2

It's not grammatical, but it's a case very similar to English headlines: Obama to win elections.

Answer 3

It's not acceptable in formal writing, but we do that all the time. You cannot say it's incorrect. It is not.

"Salida coches" and "Venta garage" is perfect Spanish for a sign. I'm punctilious (we all at StackExchange are, aren't we?) and, if I'm writing a report, the heading would be "Notificación de enfermedades infecciosas": I would never dream of omitting the "de". But in a file where I keep some documents I would write "Notificación enfermedades infecciosas" as a matter of course.

Eduardo is right: it's a case very similar to English headlines.

I don't think Diego Mijelshon is right. Spanish language is more flexible than that. You can omit the "de" in a sign or in a "post-it". "Salida coches" in a sign is natural Spanish. I think this is an important point.

I have voted up Eduardo's answer and down Diego Mijelshon's one. You can consider my answer as an expansion of Eduardo's one. It was just too long for a comment.

This was a great question.