Off the top of my head:

It could be a general signal that you are willing to ignore nonsensical social rules - this is a dominance/confidence signal, in most cases, that you either have the social standing to not be questioned about such a decision, or are confident that you have the correct skills to defend yourself if confronted, or both.

It could be a signal that you value convenience above appearing normal, assuming that you value appearing normal at all. It could also be a signal that you value appearing unusual. Further context would be useful in determining which.

It could be a signal that you belong to a particular group, most likely the group from which you got the idea to use the bag. This could be true even if those around you are unlikely to recognize the signal - it can still be a self-signaling mechanism, or a 'secret password' type signal that would increase your chance of meeting other members of the group who may live near you, or a recruitment mechanism ('conversation starter'), or some combination of those.

It could be a specific signal that you reject heteronormative limitations - I refused to carry a purse for a long time out of a combination of that and generalized rebelliousness.