Jim Harbaugh's a man of his word ... fulfilling a promise he made to ink his body if they won a national championship -- and his players filmed the whole experience. The Michigan Wolverines football team met up Saturday to receive their national championship rings ... and, JH lived up to his end of the deal -- sitting down with an artist and getting the Michigan "M" tatted on his right arm. After Michigan defeated the Washington Huskies in the title game 34-13 back in January, Jim revealed he'd promised his team he'd tattoo their logo with the record "15-0" as a shout-out to their accomplishment. Welp, no one can accuse Harbaugh of being all talk 'cause his star cornerback Mike Sainristil -- who many expect to go top 50 in this year's draft -- took a vid of the tattoo session ... but, Jim doesn't look like he's loving it. Check out the clip ... Harbaugh's got a pretty discontent look on his face -- not surprising given it's his first tattoo. He's staring down the camera the whole time, only cracking a grin once it seems the tattoo's finished up. It's a ceremonial end for Harbaugh who took the head coaching gig for the Los Angeles Chargers shortly after pulling off the immaculate season. BTW ... some upset fans are coming after Harbaugh on X 'cause cheating allegations marred the 15-0 season. Remember, Jim served a three-game suspension for a sign-stealing scandal despite expressing his innocence. Looks like Jim's tuning out the haters though ... proudly brandishing his team's accomplishment in a permanent way.