Julie would notice that Cipher isn't within her scanning range anymore. This wouldn't be conclusive given that Cipher can phase, invisibility would still be detectible by Julie and Matt given their 'Sight' isn't based on visible light, but phasing would cancel out both fairly effectively. My girl would certainly notice as, being another Xaviers mutant, there is a certain kinship. For Firestar too, but Julie isn't fully aware of that connection at this point in that case.