When an ISTP (Introverted, Sensing, Thinking, Perceiving) is mad, there are several signs and behaviors that you can observe. It's important to note that each individual is unique, and their expressions of anger may vary. However, here are some common indicators that an ISTP might display when they are upset:

1. Withdrawal: ISTPs tend to be introverted and prefer to process their emotions internally. When they are mad, they may withdraw from social interactions and isolate themselves. They might spend more time alone or engage in solitary activities to calm themselves down.

2. Silent Treatment: ISTPs are not typically vocal about their emotions, especially when they are angry. They may choose to remain silent and avoid discussing the issue that has upset them. They might also become unresponsive or give short, curt answers when spoken to.

3. Increased Bluntness: ISTPs are known for their direct and straightforward communication style. When they are mad, they may become even more blunt and straightforward in expressing their dissatisfaction. They might not sugarcoat their words and may come across as harsh or critical.

4. Physical Tension: ISTPs often have a strong connection with their physical senses. When they are angry, you may notice signs of physical tension, such as clenched fists, tightened jaw, or a rigid posture. They may also display restlessness or fidgeting.

5. Focus on Problem-Solving: ISTPs are logical and analytical thinkers. When they are mad, they tend to shift their focus towards finding practical solutions to the issue at hand. They may become more determined and persistent in resolving the problem rather than dwelling on their emotions.

6. Need for Space: ISTPs value their independence and personal freedom. When they are mad, they may need some time and space to process their emotions and regain their composure. They might prefer to be left alone until they are ready to discuss the issue or resolve the conflict.

7. Direct Confrontation: While ISTPs generally avoid unnecessary conflicts, when they are pushed to their limits, they may confront the source of their anger directly. They can become assertive and express their grievances in a straightforward manner, without mincing words.

8. Temporary Impulsiveness: ISTPs have a spontaneous and adaptable nature. When they are mad, they may exhibit impulsive behavior that is out of character for them. This could include making hasty decisions, engaging in risky activities, or expressing anger in a sudden outburst.

It's important to remember that these signs are generalizations and may not apply to every ISTP. Additionally, it's crucial to approach an angry ISTP with empathy, respect their need for space, and communicate calmly and directly to resolve any conflicts.