Has anyone seen this "R" signature before? I have no clue what the "R" stands for. Thank you in advance. Best regards.

No problem. Your interpretation of my post is correct: the necklace has a G-shaped clasp that copies Givenchy, but it does not have the Givenchy logo stamped which tells us it's a knockoff. Regarding the bracelet: I cannot speak to authenticity. You said you already confirmed authenticity elsewhere so that's great.