Privezak za lomljiv prtljag je pažljivo obeležen.

Literally, privezak can mean something attached or hanging, so in different contexts it can be a pendant, charm, tag, or attachment.

In this sentence, it most naturally means a tag or label-type attachment for luggage, not jewelry. Context is what decides the exact English equivalent.

Here za means for, and with that meaning it normally takes the accusative.

So:

• za
  • accusative = for
• prtljag is in the accusative here

The useful thing to notice is that prtljag has the same form in the nominative and accusative, because it is a masculine inanimate noun. So even though the case changes grammatically, the word itself does not change in form here.

Lomljiv means breakable, fragile, or easily broken.

It comes from the verb lomiti / slomiti, related to breaking. So lomljiv prtljag is baggage that should be handled as fragile.

A very important contrast:

• lomljiv = breakable / fragile
• slomljen = broken

So this sentence is not saying the luggage is already broken; it says it is the kind of luggage that can easily be broken.

Grammatically, prtljag is singular.

Even though English luggage/baggage can refer to multiple items, Serbian prtljag is treated as a singular mass/collective noun. That is why the adjective is also singular:

• lomljiv prtljag
  not
• lomljivi prtljag

Because obeležen agrees with privezak, which is masculine singular.

So the participle/adjective must also be masculine singular:

• privezak → masculine singular
• obeležen → masculine singular

If the noun were feminine, you would get obeležena.
If it were neuter, you would get obeleženo.

Yes. This is a passive-type construction.

• je = is
• obeležen = marked / labeled

Together, je obeležen means is marked or has been marked, depending on context. In English, the most natural translation is often just is marked/labeled.

So the structure is similar to:

• Vrata su zatvorena. = The door is closed.
• Privezak je obeležen. = The tag is marked.

In other words, the sentence focuses on the state/result, not on who did the marking.

Because pažljivo is an adverb, and it describes how the marking was done: carefully.

Compare:

• pažljiv = careful (adjective, describes a person or thing)
• pažljivo = carefully (adverb, describes an action)

So:

• pažljiv čovek = a careful man
• pažljivo obeležen = carefully marked

Because je is a clitic, and Serbian clitics usually go in second position in the clause.

That does not always mean after the first single word. It often means after the first whole phrase/unit.

Here, the first unit is the subject phrase:

• Privezak za lomljiv prtljag = one noun phrase

So the clitic comes after that whole phrase:

• Privezak za lomljiv prtljag je pažljivo obeležen.

That placement is completely normal Serbian.

Yes. Serbian word order is fairly flexible, because case endings and agreement already show the grammatical relationships.

This sentence has a neutral, natural order. But other orders are possible for emphasis, for example:

• Pažljivo je obeležen privezak za lomljiv prtljag.
• Privezak je za lomljiv prtljag pažljivo obeležen.

These alternatives may shift emphasis or sound more marked, but they are still understandable. The original sentence sounds like a straightforward neutral statement.

Yes, both can work, though the nuance may vary slightly by context.

• obeležen = marked, labeled, identified with a mark
• označen = marked, designated, labeled

In everyday usage, both can be used for tags, labels, and marked items. In some contexts, one may sound a little more idiomatic than the other, but obeležen is perfectly understandable here.

Yes. In Serbian, the same sentence in Cyrillic is:

Привезак за ломљив пртљаг је пажљиво обележен.

Serbian regularly uses both scripts, Latin and Cyrillic, and they represent the same language.