At this rate, Justin Bieber is going to be completely covered by the end of the year!For the third time this month, the 18-year-old has unveiled a new tattoo. The ink addict’s latest, which he showed off Monday, is of Roman numerals – I, IX, VII, and V – which presumably stands for 1975 … though a math teacher would wisely note that the year would technically be MCMLXXV.So what is the significance behind 1975, which now has a permanent and prominent spot on the teen idol’s right collarbone?Well, it turns out Bieber is a huge mama’s boy. The disco-era year is the one in which his mother, Pattie Mallette, was born. And the mother and son share a special bond – in her recent book, "Nowhere But Up: The Story of Justin Bieber’s Mom,” Mallette talked about becoming pregnant at the age of 17 and opting not to abort the baby, despite being encouraged to do so.There is also a vague connection to Selena Gomez. The "Spring Breakers” star, whose on-again, off-again relationship with the singer is pure teen drama, had Roman numerals – LXXVI – etched on the nape of her neck in September. At the time, she said it was a tribute to a family member – and it didn’t take Benedict Cumberbatch’s "Sherlock” character to figure out that her mother, Mandy Teefey (who was also a teen mom, giving birth to Gomez when she was 16), was born that year.Because things between Bieber and Gomez are currently in the off phase, there is speculation that his ink could be some kind of public message he’s sending her because he has been more than happy to show it off! On Monday – hours after Gomez was seen hanging out with other young Hollywood stars, including "The Hunger Games” star Josh Hutcherson, at Golden Globes parties – Bieber tweeted an attention-seeking shirtless photo of himself in the process of getting the tattoo.