Kapıcı, “Asansörü kullanmayın,” diye uyarı yaptı; emniyet için merdivenden indik.

Diye is a quotative linker meaning “saying/that.” It connects the quoted words to a reporting verb. Here it links the quoted command to the act of warning: Asansörü kullanmayın, diye uyarı yaptı. You’ll see diye after verbs like demek, söylemek, düşünmek, bağırmak, uyarmak.

It can also mark purpose or reason in other contexts:

• Purpose: Üşümeyeyim diye ceket giydim. (I put on a jacket so I won’t get cold.)
• Cause/complaint: Geç kaldın diye kızdı. (He got angry because you were late.)

Both are correct, with a nuance difference:

• Uyardı = “(he/she) warned” (simple, direct verb; very natural).
• Uyarı yaptı = “(he/she) made a warning” (lightly more formal or report-like). Other natural options:
• Uyarıda bulundu (formal)
• İkaz etti (somewhat formal/literary) With a quote, the concise and very common version is: Kapıcı, Asansörü kullanmayın, diye uyardı.

Accusative marks a definite/specific direct object. Negation doesn’t block the accusative. Here, asansörü means “the (specific) elevator” (e.g., the building’s elevator).

• Definite: Asansörü kullanmayın. (Don’t use the elevator.)
• Indefinite/generic: Asansör kullanmayın. (Don’t use elevators / Don’t use an elevator.)

Kullanmayın is the 2nd person plural imperative, which also functions as polite singular. It can address:

• multiple people, or
• one person politely/formally. On signs or in very formal contexts, you may see kullanmayınız (even more formal/polite). Informal singular would be kullanma (“don’t use” to one person you’re close to).

The ablative -den marks the route or path you move along/through: merdivenden inmek = “to go down (via) the stairs.”

• merdivene (dative) would mean “onto the stairs” (not what we want).
• merdiveni (accusative) would mark a definite direct object (not appropriate with inmek here).

Both are acceptable:

• merdivenden indik (singular) — treating “stairs” as a unit; fully natural.
• merdivenlerden indik (plural) — also common, emphasizes “the steps/staircase” as multiple steps. Everyday speech may favor the plural slightly, but there’s no real difference in meaning.

The past tense suffix is -DI, and its initial consonant assimilates to the voicing of the preceding sound:

• After a voiced sound (like n), it stays -di: in- + -di + -k → indik.
• After a voiceless sound, it becomes -ti: koş- + -ti → koştu; bak- + -tı → baktı.

A semicolon is a good choice to join two closely related independent clauses, especially when the first clause already contains an internal comma. Alternatives:

• Period: … diye uyarı yaptı. Emniyet için merdivenden indik.
• Conjunction: … diye uyarı yaptı ve emniyet için merdivenden indik. Avoid just a comma between two full clauses (comma splice).

Standard style (TDK) places the comma outside the closing quotation mark when it belongs to the main sentence, not the quoted words:

• Asansörü kullanmayın, diye uyarı yaptı. You’ll often see it inside in everyday writing, but the standard recommendation is outside.

Both are fine, with a nuance difference:

• Asansöre binmeyin = “Don’t get on/use the elevator” (literally “don’t board” the elevator), very idiomatic for elevators, buses, etc.
• Asansörü kullanmayın = “Don’t use the elevator” (more general “use”). In a building warning, either works; binmek is very natural for elevators.

Both mean “for safety,” but:

• güvenlik is the everyday word for “safety/security.”
• emniyet is more formal/institutional and is also the word for the national police force (Emniyet). So güvenlik için sounds a bit more colloquial; emniyet için feels a touch formal. Both are correct.

Yes. Common options:

• Use a colon: Kapıcı uyarı yaptı: Asansörü kullanmayın.
• Use the verb “dedi” instead: Kapıcı, Asansörü kullanmayın, dedi. If you use uyardı, it’s most natural to keep diye: Kapıcı, Asansörü kullanmayın, diye uyardı.