Shaykh Bin Baaz رحمه الله was asked the following question:
An inquirer from Riyadh asks: “Is there a mark that appears on a worshiper’s forehead called “the mark of praying”?
“A mark on the forehead may appear on the forehead of some people as a result of Sujud (prostration). Allah (Glorified and Exalted be He) describes the Sahabah (Companions of the Prophet) in Surah (Qur’anic chapter) Al-Fat-h:
Muhammad is the Messenger of Allah, and those who are with him are severe against disbelievers, and merciful among themselves. You see them bowing and prostrating (in prayer), seeking Bounty from Allah and (His) Good Pleasure. Their marks (i.e. of their Faith) are on their faces (foreheads) as a result of (their) Prostration (during Salah). This is their description in the Tawrah (Torah). And their description in the Injil (Gospel) is like a (sown) seed which sends forth its shoot…”
End quote. [Reference]
In the following audio, Ash-Shaykh Saalih al-Fawzaan hafidaho-Allah mentions that the aforementioned mark has no significance to mean the person is righteous or performs a lot of sujood
One of the shuyookh once mentioned they saw an individual who is تارك الصلاة, meaning one who doesn’t pray at all have that mark on his forehead.
Shaykh Muhammad bin Saalih رحمه الله mentions the correct meaning of the verse concerning the traces of prostration on the face is النور light and radiance of faith. And Allaah knows best.
AbdulFattaah Bin Uthman