stealthy, hugger-mugger, covert, undercover, furtive, cloak-and-dagger, hole-and-corner, clandestine, sneaky, on the quiet, more...

overt, flagrant, blatant, conspicuous

covert, subtle, stealthy, sneaky, clandestine, underhanded, furtive, backhanded, more...

furtive "yo!",   done in secret,   sneaking unseen,   trying to be hide