haengsa jeone myeongchareul boyeo juseyo.

전에 means before in time.

After a noun, the pattern is:

• Noun + 전에 = before N

So:

• 행사 전에 = before the event

You can also use 전에 after a verb phrase:

• 가기 전에 = before going
• 먹기 전에 = before eating

In this sentence, 행사 전에 tells you when you should show the badge.

Because Korean normally uses Noun + 전/전에 directly.

So the natural pattern is:

• 회의 전에 = before the meeting
• 수업 전에 = before class
• 행사 전에 = before the event

Using 의 here would sound unnatural. English often needs of-type wording, but Korean does not in this pattern.

명찰 means a name tag or name badge.

It usually refers to something you wear on your clothes at:

• events
• conferences
• schools
• workplaces

A useful comparison:

• 명찰 = name tag / badge
• 명함 = business card

So this sentence is about showing a badge, not handing over a business card.

을/를 is the object marker in Korean. It marks the thing that the action is done to.

Here, the thing being shown is 명찰, so it gets the object marker:

• 명찰을

Because 명찰 ends in a consonant, it takes 을.

Rule:

• consonant ending → 을
• vowel ending → 를

These mean different things:

• 보세요 = please look
• 보여 주세요 = please show

That difference is very important here.

The sentence is not telling someone to look at the badge. It is telling them to show the badge.

보여 주세요 comes from 보여 주다, which means to show or literally to let someone see.

Korean often leaves out information that is obvious from context.

In this case, the sentence does not explicitly say who should see the badge, because it is understood from the situation. It usually means something like:

• show it to the staff
• show it to us
• show it to the person checking entry

English often says this more explicitly, but Korean commonly omits it.

It is a polite and common request form.

The pattern -아/어 주세요 means please do ... in a polite way. It is very common in everyday Korean, customer service, signs, and announcements.

Comparison:

• 보여 줘 = casual
• 보여 주세요 = polite
• 보여 주십시오 = more formal

So 보여 주세요 is polite without sounding overly stiff.

Because Korean often omits the subject when it is clear from context.

In English, you would usually say something like:

• Please show your badge before the event.

The hidden subject in Korean is basically you or attendees, but Korean does not need to say it if everyone already knows who is being addressed.

This is very normal in Korean.

In standard spacing, 보여 주세요 is usually written as two words.

That is the safer standard form to learn and use.

You may sometimes see:

• 보여주세요

in casual writing, messages, or signs, but 보여 주세요 is the better standard spelling for learners.

Yes, sometimes 행사 전 can appear, but 행사 전에 is the clearer adverbial form in a sentence like this.

Compare:

• 행사 전 안내 = pre-event guidance / guidance before the event
• 행사 전에 명찰을 보여 주세요 = Please show your badge before the event.

So 전 often appears in noun-style expressions, while 전에 is very natural when describing when an action happens.