Yellow Card For Lying

[Retrozetti]

Though MCBear's comments are almost point on, I would strongly discourage you from "request(ing) to see what is under the tape." You have to trust their answer. [07'-08' Case Book 4.1.6 Situation B(comments)] Having that said, if the jewelry becomes exposed during the game, then you caught them in their deception, and it's an immediate Red Card for unsporting conduct or Yellow & Red Card for "flagrant unsporting conduct." Never lie to the ref!

Step-by-step, given your situation, I would:
1) Upon noticing the bracelets, ask the player to step off of the court (never touch any player or coach), inform the player that "jewelry is not allowed on the court during warm-ups and/or competition, those bracelets are considered jewelry... so please remain off the court while you are wearing jewelry." Never tell them to remove their jewelry, you don't have that authority, but you do have the authority to to prohibit them from stepping onto the court while wearing jewelry. [Rule 4.1 Penalties]
2) At the captains meeting, you notice "possible" taped-over bracelets. Using preventative officiating, you can remind them that tape over bracelets is not acceptable, so if there are bracelets under the tape, the player will not be allowed on the court. Also, if during your captains meeting the player is standing "on the court," you certainly should ask the player if they have bracelets under the tape, because if they are wearing jewelry, then they shouldn't be on the court. [07'-08' Case Book 4.1.5(b)] No card would be required if they step off the court and acknoweldged that they will remain off the court until their uniform is made legal.
3) You ask the player, and they say that they are not wearing jewelry. You have to trust their answer. [07'-08' Case Book 4.1.6 Situation B(comments)] "Unless it is obvious there is jewelry present, officials need not look under tape to see if there is jewelry..." However, when you mentioned that the Referee "checked the tape an felt the bracelets", never never never touch a player, not even for court injuries... only for "life-saving measures" or to "determine if a player is unconscious or apparently unconscious." [Rule 3.3.18]
4) Assuming this match is for high school (NFHS), after your preventative officiating, if they were still wearing the bracelets (but didn't respond to your concerns in a deceptive manner), it would be an IYC (unsporting conduct). [Rule 4.1 Penalties] Or no card if they either: remained off the court, or moved off the court with the intent to make their uniform legal before entering the court.
5) However, after your preventative officiating, if they were still wearing the bracelets and lied to you about it being under the tape, you have the discretion to sanction with an IRC (unsporting conduct - serious offense) or IY&RC (Individual Yellow & Red Card: unsporting conduct - flagrant offense). [Rule 12 Penalties (a) (b) & (c)] However, an IY&RC is an extreme sanction for this situation. Officiating is not about "I caught ya" nor "one-bullet Barnie's"... instead, preventative officiate, communicate to the players coach about your concern, and protect the "enjoyment of the sport."