I would agree that any such bag should be small enough to make it clear that you are not carrying a laptop, since such attract thieves.
I try to avoid carrying around my laptop, but when I have to, I use a cheap shopping bag, never a proper laptop bag for that reason.
My situation is funny because I DON'T carry a laptop but I like to use laptop bags for work ( I like their design ). That results in double stress : fear from theives , and frustration of my colleagues false envy. Some of them think the boss has granted me a laptop !!!
Just in case anyone is interested, here is may favourite design for work bag. It opens completely and EVERYTHING is accessible. Papers, pens ..everything is in front of you. There is a lowere zippered pocket at the bottom for papers that you don't need all the time. I use that for contact numbers, reference sheets ..etc.
There is another zippered pocket in the bag's cover ( cannot be seen in the pic becasuee of open cover ) . This pocket I use for some prep items like flashlight and small folding knife ..etc. )
Mine looks like this one, has no laptopb, although most everyone assumes there is one inside !!!