Learn Spanish (Latin America): Pon la furgoneta aquí sin que la policía sospeche. - Put the van here without the police suspecting.

The conjunction sin que (without) introduces an outcome that the speaker wants to avoid. Because the police suspecting is a hypothetical event that you are actively trying to prevent, Spanish requires the subjunctive. In fact, sin que belongs to a specific group of conjunctions that always trigger the subjunctive.

Why can't we just use the infinitive and say sin la policía sospechar?

You use sin plus an infinitive only when the subject is the same for both actions, like in Lo hice sin pensar (I did it without thinking). Because the subject here changes from tú (putting the van) to la policía (suspecting), you must use the conjugated sin que structure.

What verb form is pon?

Pon is the irregular affirmative informal command (imperative) for tú of the verb poner. As a quick refresher: if you were telling someone NOT to put the van there, you would use the negative command, which switches to the subjunctive form: no pongas.

Why does policía use a singular verb here?