Das Verkehrszeichen vor der Kreuzung ist neu, und ich habe es zuerst nicht erkannt.

Because Verkehrszeichen is a neuter noun.

A useful rule for German compound nouns is:

• the last part usually decides the gender
• Verkehrszeichen ends in Zeichen
• das Zeichen is neuter

So the whole compound is das Verkehrszeichen.

It is a compound noun, which German uses very often.

It is made up of:

• Verkehr = traffic
• Zeichen = sign / symbol

So Verkehrszeichen is literally a traffic sign.

The -s- in the middle is a linking sound (called a Fugen-s). It does not usually need to be translated; it just helps connect the parts of the compound.

Because vor is a two-way preposition.

Two-way prepositions take:

• dative for location
• accusative for movement toward a place

Here, the sentence describes where the sign is: it is before the intersection. That is location, so German uses the dative:

• vor der Kreuzung

Also, Kreuzung is a feminine noun:

• die Kreuzung
• dative: der Kreuzung

Compare:

• Das Verkehrszeichen steht vor der Kreuzung. = location
• Ich stelle das Schild vor die Kreuzung. = movement/placement

Most naturally, it describes the sign.

So the structure is basically:

• Das Verkehrszeichen vor der Kreuzung = the traffic sign before the intersection
• ist neu = is new

In other words, the whole subject is the traffic sign before the intersection.

Because neu is a predicate adjective here, and predicate adjectives do not take endings in German.

After verbs like:

• sein = to be
• werden = to become
• bleiben = to remain

the adjective stays in its basic form:

• Das Zeichen ist neu.
• Die Straße ist breit.
• Die Autos sind schnell.

But before a noun, it would take an ending:

• das neue Verkehrszeichen

This is the Perfekt tense, which is very common in spoken German for talking about the past.

The verb is erkennen = to recognize.

Its perfect form is:

• ich habe erkannt

So the second clause means that the speaker did not recognize it at first.

German often prefers Perfekt in everyday speech where English might simply use the simple past.

You could also see:

• ich erkannte es zuerst nicht

That is Präteritum (simple past), which is more common in writing or narration.

Because erkennen has the prefix er-, and er- is an inseparable prefix.

Verbs with inseparable prefixes usually do not add ge- in the past participle.

So:

• erkennen → erkannt
• verstehen → verstanden
• bezahlen → bezahlt

That is why German says ich habe es erkannt, not geerkannt.

In a German main clause, the finite verb goes in position 2.

Here the finite verb is habe, so it comes early:

• ich habe ...

The past participle erkannt goes to the end of the clause:

• ich habe es zuerst nicht erkannt

This is a very common German pattern:

• Ich habe ihn gesehen.
• Sie hat das Buch gelesen.
• Wir haben es verstanden.

es refers back to das Verkehrszeichen.

Since Verkehrszeichen is:

• singular
• neuter

the matching pronoun is es.

It is also the direct object of erkennen, so it is in the accusative case. For a neuter singular pronoun, accusative is still es.

Because the sentence means at first, I did not recognize it.

Here:

• zuerst = at first / initially
• nicht erkannt = did not recognize

So nicht is placed before the participle it is negating.

The word order helps show that the meaning is:

• I didn't recognize it at first

rather than something like:

• I didn’t recognize it first
  (which would suggest a different contrast)

So zuerst nicht erkannt is the natural wording for this idea.

In this sentence, zuerst is the natural word for at first or initially.

That is different from erst, which often means things like:

• only
• not until
• as late as

Examples:

• Ich habe es zuerst nicht erkannt. = I didn’t recognize it at first.
• Ich habe es erst später erkannt. = I only recognized it later.

So zuerst fits the idea of an initial stage, while erst often adds the sense of only / not until.

Usually, no.

When und connects two main clauses, German often does not require a comma:

• Das Verkehrszeichen vor der Kreuzung ist neu und ich habe es zuerst nicht erkannt.

The version with the comma can appear as a stylistic choice to make the pause or structure clearer, but learners should know that German does not use commas before and as automatically as English sometimes does.