Preposed direct objects

I once saw a sign that said: Recuerda que la seguridad la hacemos todos.

Todos hacemos la seguridad is a canonically ordered sentence: subject - verb - direct object. When we move the direct object la seguridad to the beginning, Spanish grammar requires that we add a direct object pronoun la (= la seguridad) here.

More generally, when a direct object is present, it comes after the verb. Cerré la puerta. It is possible to put the object first, but in that case you must add a pronoun in the spot where a direct object pronoun normally goes. La puerta la cerré yo. I'm the one who closed the door.

• El baño lo quiero limpio. Literally, the bath, I want it clean.
• Mi carro, lo comparto con mi hermano. I share my car with my brother. (movie dialogue)

Here's an example that I overheard recently at the supermarket: Los cigarros, ¿los compro allá? The customer was already having his groceries rung up at a particular cash register. How he wanted to know if he had to go to a different one to purchase cigarettes.

When to prepose direct objects

Use this construction when the direct object is already part of the conversation. By putting the direct object first, what's new to the listener goes at the end of the utterance, where it packs more punch. Mi carro, lo comparto con mi hermano. The important information here is not that the speaker has a car but that she shares it with her brother. In the sign mentioned above, todos goes at the end because it is the new element. The previous text in the sign was all about security. The message here is that security is the responsibility of everyone.