Esse é um mau sinal.

In Brazilian Portuguese, esse often corresponds to that, but in real-life usage the line between this and that is not always as strict as in English.

So Esse é um mau sinal is very naturally translated as That’s a bad sign.

By itself, esse means that one / this one, depending on context.

Both are demonstratives, but they are used a little differently:

• esse = used like that one / this one, often standing in for a masculine noun
• isso = that / this when you are referring to an idea, statement, or undefined thing

So:

• Esse é um mau sinal. = That one / that is a bad sign.
• Isso é um mau sinal. = That is a bad sign.

Both can be possible depending on context, but esse suggests something more specific or previously identified.

For example, if someone points to a symptom, result, or event, esse can refer to that specific thing.

É is the verb ser in the he/she/it is form, and the accent is required.

• é = is
• e = and

So the accent is very important because it changes the word completely:

• Esse é um mau sinal. = That is a bad sign.
• Esse e um mau sinal. = incorrect

This is one of the most common questions learners have.

In this sentence, mau is correct because it is an adjective describing the noun sinal.

A useful shortcut:

• mau is usually the opposite of bom
• mal is usually the opposite of bem

So:

• um bom sinal = a good sign
• um mau sinal = a bad sign

But:

• ele está bem = he is well
• ele está mal = he is unwell / he is bad

Important: in most Brazilian accents, mau and mal sound the same, so you usually have to rely on grammar and meaning to know which spelling is right.

Because mau has to agree with sinal, and sinal is a masculine singular noun.

Agreement works like this:

• masculine singular: mau
• feminine singular: má
• masculine plural: maus
• feminine plural: más

Examples:

• um mau sinal = a bad sign
• uma má ideia = a bad idea
• maus hábitos = bad habits
• más notícias = bad news

Because Portuguese usually uses an article here just like English does:

• um sinal = a sign
• um mau sinal = a bad sign

So Esse é um mau sinal is literally That is a bad sign.

You usually would not drop um here in normal neutral speech.

Sinal can mean several related things, including:

• sign
• signal
• mark
• indication

In Esse é um mau sinal, it means sign in the sense of an indication that something may be wrong.

So this sentence is about interpretation, not about a traffic signal or electronic signal.

A rough Brazilian Portuguese pronunciation is:

EH-see eh oong mow see-NAW

A few notes:

• Esse sounds roughly like EH-see
• é sounds like eh
• um is nasal; in natural speech it may sound closer to ũ
• mau sounds roughly like mow or like the ow in cow with an m in front, depending on how you approximate it
• sinal ends with a sound like naw in most Brazilian accents

Also, in connected speech, esse é often flows together smoothly.

Yes, absolutely. Isso é um mau sinal is also natural.

The difference is mainly about what you are pointing to:

• esse refers more to that one / that specific thing
• isso refers more to that / what you just said / that situation

So if someone says something worrying, you might reply:

• Isso é um mau sinal.

If you are pointing to a specific symptom, result, or event, you might say:

• Esse é um mau sinal.

In everyday Brazilian Portuguese, both can be heard depending on context.

Yes, it is completely natural.

Esse é um mau sinal is a normal way to say that something suggests a negative outcome or a problem.

Very common alternatives include:

• Isso é um mau sinal.
• Isso não é um bom sinal. = That’s not a good sign.
• Esse não é um bom sinal.

All of these sound natural in Brazilian Portuguese.