Learn Hardcore Korean: chekeu-inhal ttae hotel peureonteueseo seomyeonghae juseyo. - Please sign at the hotel front desk when checking in.

The pattern -ㄹ/을 때 means “when (you) do X.” Here, 체크인하다 (“to check in”) becomes the attributive 체크인할 + 때 (“time/moment”), giving “when you check in.”

Why is there no space in 체크인할 때 (not “체크인 할 때”)?

Because 체크인하다 is treated as a single verb (“to check in”). In 체크인할 때, the verb is in attributive form (-할) modifying 때, so you don’t separate 체크인 from 할. Compare: 먹을 때, 갈 때, 운전할 때—no space before -할/-을.

Why use 에서 in 호텔 프런트에서, not 에?

-에서 marks the place where an action happens. Signing is an action, so 프런트에서 is natural.
-에 marks a static location/existence or direction. You might use -에 with verbs like “있다/없다” (e.g., 프런트에 사람이 많아요), but for “sign,” use -에서.

Is 프런트 the right word? I’ve seen 프론트 and other terms.

The standard spelling is 프런트 (hotel front desk). You’ll also hear:

프런트 데스크, 리셉션 (reception), 안내 데스크.
프론트 is common colloquially but nonstandard. In hotels, 프런트 alone usually implies the hotel front desk; 호텔 just makes it explicit.

What’s the nuance difference between 서명 and 사인?

서명 is the proper/official word for a signature (legal/administrative contexts). Hotels commonly use this.
사인 is a loanword; everyday speech uses it for “signature,” but strictly it often means an autograph from a celebrity. In formal contexts, prefer 서명.

Do I need an object marker, like 서명을 해 주세요?

Both are fine:

서명해 주세요 treats 서명하다 as a single verb (“please sign”).
서명을 해 주세요 splits the Sino-Korean noun + 하다 (“please do a signature”), adding the object marker -을. It’s also correct and slightly more explicit. You can also add a location target: 여기에 서명해 주세요 (“Please sign here”).

What politeness level is 서명해 주세요, and how can I make it more formal or softer?

서명해 주세요 is polite (해요체) and already includes the honorific -시- inside 주세요.
More formal/service-language: 서명해 주십시오.
Softer/more tentative: 서명해 주시겠어요? or 혹시 서명해 주실 수 있을까요?
To honor the listener’s action in the time clause, you can say 체크인하실 때.

Can I say 체크인 시 instead of 체크인할 때?

Yes, in formal written notices or signs: 체크인 시 프런트에서 서명해 주십시오. Here -시(時) is a Sino-Korean noun meaning “at the time of.” It sounds official/formal.

Is the word order fixed, or can I move parts around?

Time and place phrases are flexible as long as they come before the verb. For example:

체크인할 때 호텔 프런트에서 서명해 주세요. (original)
호텔 프런트에서 체크인할 때 서명해 주세요. (emphasizes location first)
체크인하실 때는 호텔 프런트에서 서명해 주세요. (topic -는 adds emphasis/contrast on “when checking in”)

Should I write 서명해 주세요 or 서명해주세요?

Standard spacing treats -아/어 주다 as an auxiliary verb, so write it separately: 서명해 주세요. You’ll often see the fused 서명해주세요 in casual contexts, but for formal writing or tests, prefer the spaced form.

Why use -할 때 and not something like 동안 or 중?

-할 때 = at the moment/when something happens (“when you check in”).
-하는 동안 = throughout the duration (“while you are doing X”), which doesn’t fit a brief action like check-in.
-중 is used for “in the middle of” as a noun phrase: 체크인 중입니다 (“We are checking in”), not for “when.”

Any pronunciation tips for this sentence?

체크인할 때 is pronounced roughly “che-keu-in-hal tte” (the 때 is a tense sound).
프런트 has the vowel -런- (not “론”): “peu-reon-teu.”
In 서명해 주세요, each word is clear; no special assimilation beyond normal linking.

Is 호텔 necessary before 프런트?

Not strictly. 프런트 by itself typically implies the hotel front desk in hotel contexts. Adding 호텔 avoids ambiguity and sounds a bit more explicit or careful. In non-hotel venues, you’d usually say 안내 데스크 or 접수처, not 프런트.

Could I say 체크인 때?

It’s understandable, but native preference is 체크인할 때 in conversation, or 체크인 시 in formal notices. X + 때 is fine with many native nouns (e.g., 점심 때, 퇴근 때), but with loanword actions like 체크인, -할 때 sounds more natural.