Short answer: The “flower on the chest” you see on many Tirthankara images is typically the Shrivatsa, one of the eight auspicious symbols (Ashtamangal) described in Jain scriptures. It represents purity of knowledge and spiritual excellence.

What it means in Jainism (arth)

• Shrivatsa is a special mark that appears on the chest of the Jina (the Tirthankara). It is taken as a sign of pure, enlightened knowledge that the Tirthankara has attained.
• It is one of the Ashtamangala, the eight sacred symbols used in Jain tradition to indicate the presence and auspiciousness of a Tirthankara. Devotees often trace or draw Shrivatsa as part of ritual worship and iconography. ( jainknowledge.com)
• In some depictions the mark can look like a flower or a decorative knot, but its core meaning remains “pure, realized knowledge from the heart.” ( jainknowledge.com)

Tradition differences (Digambar vs Śvetāmbara)

• The Shrivatsa symbol is widely acknowledged in Jain iconography and is commonly shown on Tirthankara images across traditions. The exact artistic style of Shrivatsa (shape or placement) can vary slightly by region or temple, but the meaning as a mark of enlightened knowledge is preserved.
• Other Ashtamangal symbols (like the lotus in some lists) are also part of the same symbolic framework, but Shrivatsa specifically is one of the heart-centered marks. If you want, I can point out how Digambar and Śvetāmbara depictions differ in a particular Tirthankara’s image.

You can read more about Shrivatsa as part of Ashtamangal here and in the description of Ashtamangala symbols here .

Note: If you’d like, I can summarize the exact 8 Ashtamangala and which Tirthankaras they are commonly associated with.