What are the widespread errors and innovations (bid'ah) in prayer, such as adding "ta'alayta" (You are exalted) in the dhikr or saying "wa 'alaykum as-salam" (and upon you be peace) after "Allahumma Antas-Salam wa minkas-salam" (O Allah, You are As-Salam [the Giver of Peace], and from You comes all peace), that could be written on a sign to be hung in the mosque to combat these innovations?

Adding (and You are exalted) after the prescribed remembrance "O Allah, You are As-Salam, and from You is all peace, blessed are You, O Possessor of Majesty and Honor" is not part of the Sunnah. It is preferable to adhere to the wording that has been reported. However, it is not considered an innovation in itself, as it has been reported in other hadiths. As for saying "Wa 'alayka as-salam" (and upon you be peace) in the Tashahhud, this is contrary to the Sunnah, as the Prophet (peace and blessings of Allah be upon him) forbade it. Creating a chart to explain violations and innovations is a good and commendable project. To identify common violations in a specific mosque, one can refer to specialized books such as "Al-Qawl Al-Mubin fi Akhta' Al-Musallin" (The Clear Statement Regarding the Mistakes of Worshippers).