In Jainism, a Tirthankar is identified by a specific sign (lanchhan or emblem) on or beneath his idol. This emblem helps distinguish the 24 Tirthankaras and tells devotees who that Jina is. There are also differences in how idols are presented in Digambar and Śvetāmbar temples, but the core idea remains: each Tirthankar has a unique sign and a distinctive posture.

Key points:

• Every Tirthankar has a unique emblem (lanchhan) that appears on the base of the idol or beneath it. This emblem is the quick identifier of that Tirthankar. For example, the emblem for Mahavira is the lion, and other Tirthankaras have other symbols (bull, elephant, lotus, swastika, etc.). ( jainknowledge.com)
• In addition to the emblem, many traditions reference a birthmark on the right thigh that corresponds to the Tirthankar’s sign on the idol. The emblem and the birthmark together help devotees recognize the Jina. ( jainknowledge.com)
• Iconography can vary between Digambar and Śvetāmbar traditions in how idols are presented (e.g., eye depiction and styling), but the lanchhan system remains the standard identification method. ( jainknowledge.com)
• The 24 Tirthankaras (in order) each have their own symbol, which is widely used in temples, art, and scriptures to identify them. A complete list of these symbols is provided in Jain sources. ( jainknowledge.com)

If you’d like, I can list all 24 Tirthankaras with their specific emblems.

You can read more here and here