Nemojte da ostavite člansku kartu u ormariću.

Nemojte is the polite/plural form of nemoj, and in this kind of sentence it means don’t.

So Nemojte da ostavite... means Don’t leave...

It can be used:

• for more than one person
• for one person politely/formally

In Serbian, a very common way to make a negative command is:

• nemoj / nemojte + da + verb

So here:

• Nemojte da ostavite = Don’t leave

The word da does not really mean that here in the usual English sense. It is just part of this command structure.

Ostavite is the 2nd person plural present-tense form of ostaviti.

After nemojte da, Serbian normally uses this present-tense form:

• Nemojte da ostavite

Even though it is grammatically a present form, the whole expression functions as a negative command.

This is about aspect, which is very important in Serbian.

• ostaviti = perfective
• ostavljati = imperfective

Here, ostaviti is used because the sentence is warning against a single completed act: leaving the card behind in the locker.

So Nemojte da ostavite... sounds like:

• Don’t leave it there
• Make sure you do not leave it behind

A related version with the imperfective would be:

• Ne ostavljajte člansku kartu u ormariću.

That can sound more like:

• Don’t leave the membership card in the locker in a general or habitual sense.

In many practical situations, both are possible, but the aspect gives a slightly different feel.

Because this phrase is the direct object of the verb, so it is in the accusative case.

Dictionary form:

• članska karta = nominative

In this sentence:

• člansku kartu = accusative

Both words change because the adjective and noun must agree:

• članska → člansku
• karta → kartu

Članska karta literally means a membership card.

It is made from:

• član = member
• članski / članska = membership-related, member’s
• karta = card, ticket, pass

So članska karta is the normal Serbian expression for a card showing that someone is a member of an organization, gym, library, club, etc.

U ormariću is in the locative case because it expresses location: in the locker.

With u, Serbian often uses:

• locative for being in/at a place
• accusative for movement into a place

Here there is no movement into the locker. The idea is location, so:

• u ormariću = in the locker

Ormarić is a diminutive form of ormar.

• ormar = wardrobe, cabinet, closet
• ormarić = small cabinet, little cupboard, locker

In this sentence, ormarić is best understood as locker.

Yes, absolutely.

That is another very natural way to say Don’t leave the membership card in the locker.

Compare:

• Nemojte da ostavite člansku kartu u ormariću.
• Ne ostavljajte člansku kartu u ormariću.

Both are correct, but they are built differently:

• nemojte da + perfective verb often focuses on not doing one complete action
• ne + imperfective imperative often sounds more general or habitual

In everyday notices and instructions, both patterns are common.

It can be either:

• more than one person
• one person formally/politely

Because Nemojte and ostavite are 2nd person plural forms.

So this is the normal version for:

• speaking to a group
• giving a polite instruction to one person

You would say:

• Nemoj da ostaviš člansku kartu u ormariću.

This is the singular informal version.

Compare:

• Nemoj da ostaviš... = informal singular
• Nemojte da ostavite... = plural or formal singular

Yes, Serbian word order is fairly flexible, although the original sentence is the most neutral and natural here:

• Nemojte da ostavite člansku kartu u ormariću.

You could move things around for emphasis, for example:

• Nemojte da ostavite u ormariću člansku kartu.

But that sounds more marked. The original order is best for a normal instruction or notice.