Loud conversation, yelling, or calls to and from drivers of taxicabs is prohibited. The sounding of horns or other mechanical devices for purposes other than lawful traffic signals is prohibited. Drivers shall refrain from the use of profane, loud, insulting, or derogatory language and insulting or intimidating conduct while driving or operating a taxicab. Drivers shall present a neat and clean appearance at all times while on duty and shall maintain good personal hygiene. Any violation of this Section shall be grounds for suspension or revocation of a license.