sinhoga bakkwigi jeone uhoejeonhaji ma.

Here, 신호 means traffic signal / traffic light.

By itself, 신호 can mean signal in a broader sense too, but because the sentence is about 우회전 (turning right), it is naturally understood as a traffic light.

가 is the subject marker. It shows that the signal is the thing that changes.

• 신호가 바뀌다 = the signal changes
• 신호를 바꾸다 = to change the signal

So in this sentence, the signal is not being acted on directly; it is the subject of 바뀌다.

You could sometimes hear 신호는 in a different context if the speaker wants to make the signal the topic, but 신호가 is the most straightforward choice here.

바뀌기 전에 is made like this:

• 바뀌다 = to change / to be changed
• 바뀌기 = turning the verb into a noun-like form with -기
• 전에 = before

So:

• 바뀌기 전에 = before changing / before it changes

In natural English, this sentence is understood as:

• before the signal changes

This pattern is very common:

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

This is a very common Korean verb pair:

• 바뀌다 = to change, to get changed
  
  • intransitive
• 바꾸다 = to change something
  
  • transitive

So:

• 신호가 바뀌다 = the light changes
• 신호를 바꾸다 = to change the light

In your sentence, the light is the thing that changes, so 바뀌다 is correct.

우회전하다 means to turn right.

It comes from:

• 우 = right
• 회전 = turn / rotation
• 하다 = to do

So literally it is something like to do a right turn, but in natural English it simply means to turn right.

A related word is:

• 좌회전하다 = to turn left

The pattern -지 마 means don’t do ...

So:

• 우회전하다 = to turn right
• 우회전하지 마 = don’t turn right

The space is normal because 마 is written separately in this prohibition pattern:

• 가지 마 = don’t go
• 먹지 마 = don’t eat
• 우회전하지 마 = don’t turn right

So the spacing in your sentence is correct.

You can use 안 to make a statement negative, but for a negative command, Korean usually uses -지 마.

Compare:

• 우회전 안 해 = I’m not turning right / You don’t turn right
  This is not the normal way to say Don’t turn right
• 우회전하지 마 = Don’t turn right
  This is the normal prohibitive form

So if you want to tell someone not to do something, -지 마 is the usual pattern.

It is a casual / plain negative command.

It can sound:

• direct
• blunt
• natural with someone close to you
• suitable in short warnings or very plain instructions

More polite versions would be:

• 우회전하지 마세요 = Please don’t turn right
• 우회전하지 마십시오 = a more formal command style

On signs, you might also see something like:

• 우회전 금지 = No right turn

It is omitted.

Korean often leaves out subjects when they are obvious from context. In a command, the listener is understood automatically, so there is usually no need to say you.

So:

• 신호가 바뀌기 전에 우회전하지 마 naturally means
• Don’t turn right before the signal changes

Even though you is not stated, it is understood.

Yes. You can say either:

• 바뀌기 전에
• 바뀌기 전

Both mean before it changes.

The version with 전에 often feels a little fuller, but both are common and natural. In many sentences, the difference is very small.

The sentence has this basic order:

• 신호가 바뀌기 전에 = before the signal changes
• 우회전하지 마 = don’t turn right

So Korean puts the time/condition part first, then the main command last.

That is very normal in Korean. A literal breakdown would be:

• signal + changes + before + right-turn + don’t

But natural English is:

• Don’t turn right before the signal changes.