When it comes to INTJs, it can be a bit challenging to determine if they are flirting due to their reserved and analytical nature. However, there are a few signs that can help you identify if an INTJ is interested in you romantically:

1. Intellectual engagement: INTJs are known for their love of intellectual discussions and debates. If an INTJ is flirting, they will likely engage in deep conversations with you, showing genuine interest in your thoughts and ideas. They may challenge your opinions, ask thought-provoking questions, and enjoy exchanging knowledge.

2. Sharing personal insights: INTJs are typically private individuals, but if they are flirting, they may open up and share personal insights or experiences with you. This is a sign that they trust you and want to establish a deeper connection.

3. Teasing and sarcasm: INTJs often have a dry sense of humor and enjoy playful banter. If they are flirting, they may use teasing or sarcasm as a way to create a lighthearted and fun atmosphere. They might make witty remarks or engage in friendly teasing to grab your attention.

4. Quality time: INTJs value their time and tend to be selective about who they spend it with. If an INTJ is interested in you, they will make an effort to spend quality time together. They may suggest activities or outings that align with their interests, such as visiting a museum, attending a lecture, or engaging in a shared hobby.

5. Thoughtful gestures: While INTJs may not be naturally inclined towards grand romantic gestures, they may show their interest through small, thoughtful actions. They might remember details about your preferences, surprise you with a book or article they think you'll enjoy, or offer practical help when you need it.

6. Increased attention: INTJs are observant individuals, and if they are flirting, they will pay more attention to you than usual. They may maintain eye contact, lean in when you speak, and display active listening skills. They might also remember small details from previous conversations, demonstrating their attentiveness.

7. Physical proximity: INTJs are not typically touchy-feely individuals, but if they are flirting, they may subtly increase physical proximity. They might find excuses to be close to you, such as sitting or standing near you, brushing against you lightly, or initiating casual physical contact like a gentle touch on the arm.

8. Protective behavior: INTJs can be protective of those they care about. If they are flirting, they may display signs of protectiveness towards you. They might offer advice or guidance, show concern for your well-being, or step in to help when they perceive a potential threat or problem.

It's important to note that INTJs can vary in their flirting style, and not all of these signs may be present in every situation. Additionally, INTJs tend to take their time when it comes to romantic relationships, so their flirting may be subtle and gradual. It's always best to communicate openly and directly with an INTJ to understand their intentions and feelings.