Frank Cali Murder Suspect Writes 'MAGA Forever' on Hand, Under Protective Custody

2:15 PM PT -- Anthony Comello's attorney, Robert C. Gottlieb, tells TMZ that his client has waived extradition Monday and will be arraigned in a Staten Island court next week. Gottlieb also tells us that Comello has been placed in protective custody after receiving "serious threats," where he will remain while his case is pending. Gottlieb adds that Comello's family cannot believe the accusations against Anthony, and promises to get to the truth of the matter.

The man suspected of killing Gambino crime boss Frank Cali came to court with a message on his hand ... "United We Stand MAGA Forever."

Anthony Comello faced a New Jersey judge Monday and displayed his left palm with words written with a blue ballpoint pen. A court officer scoffed at Comello -- who was arrested and taken into custody over the weekend -- asking him why he was waving his hand to reporters. His response ... "Why? I'm handcuffed," suggesting he couldn't do any harm by showcasing his palm.

Our law enforcement sources said cops believe Comello may have murdered Cali because the mob boss was blocking him from dating Cali's niece.

You'll recall, domestic terrorism suspect Cesar A. Sayoc pledged allegiance to Trump ... festooning his van with tons of pro-Trump stickers and allegedly sending pipe bombs to CNN, President Obama and others.

Then there's Florida shooter Nikolas Cruz, who wore a MAGA hat during target practice just months before killing 17 people at his former high school.