The prayer may be indicated by reciting aloud

Question : And is there a third way? Yes, that is by reciting aloud.

Answer : It is permissible. So if someone asks for your permission or calls out to you while you are praying, and you raise your voice with what you are saying, that serves as a signal. But the best thing is the tasbih (praise of Allah), because the Prophet (peace and blessings be upon him) commanded it. The Prophet (peace and blessings be upon him) commanded it.