At six weeks, it's hard to tell. Everything is new to them at that age. But I suspect they make the connection very quickly. If they groom your legs or mark when climbing on them, then I'd say they've realized it's all you. It's natural for rats to be afraid of your hands, even when they trust you in general. Try pretending that your hand is another rat, and have it play with them the way they play with one another--run up to them, run away, wrestle (let them win half the time), run away and come right back--all the things that rats do to signal playfulness and a desire to engage.
Also, when you pick your rats up at that age, it is important to make them feel safe and supported. Scoop the rat gently and slowly up in both hands, making sure the whole body is supported. Then bring the rat close to your chest (
Rattus norvegicus are burrowers, and feel safest when next to a wall). Once your rats know and trust you, you will be able to pick them up any old how and they won't be frightened, but for now be careful about it.
Lastly, be sure to give them plenty of treats, so that they associate your hands with good things. Puffed rice or wheat makes a good treat for this purpose, because you can give the rats quite a lot without filling them up and ruining their diet. Also, if you put a dab of something yummy on your finger and let the ratties lick it off, that will help reinforce the message.
Good luck, and enjoy your ratties--six weeks is a fun age.

P.S.--Forgot to mention that baby rats don't like to be held for very long at a time--they have too much energy to sit still for much cuddling. So don't be disappointed if they don't want to stay in your hands, just get them used to being picked up and let them run off and do what a rat's gotta do.