Does anybody here know the lawful way to transport a handgun while on motorcycle here in SoCal? I searched and couldn’t find a clear answer online, haven’t called a lawyer, and figured somebody here might know the legal method of transporting a handgun while on motorcycle, so here I am asking. I understand that whatever is posted here is not legal advice and nobody here is my lawyer, I’m just trying to get a rough understanding of it.
I have a crotch rocket and I would like to hit up my local range to get some trigger time with my handgun, but don’t want to get busted for unknowingly committing a crime and possibly getting my right to own a gun taken from me. I figure if I have it unloaded in a locked container in my backpack I should be good to go since it’s not easily accessible, but Im not sure if that’s illegal. Can anybody here shed some light?

When I lived in CA I use to transport a handgun either in a tank bag or a back pack. I threw on one of those TSA approved combo locks on the zippers. It was a locked container so it met the rules as far as I was concerned. I was never pulled over so I was never asked about having any weapons.  No, I'm not a lawyer and have never stayed in a holiday in express so my advice is worth zilch.

Not sure how this works fully but once not transporting the handgun on/in the vehicle (unloaded in the locked container), one is apparently supposed to go directly to/from the lawful purpose.  That said, it's hard to find the specific requirement for that, it seems to be mentioned along with the discussions of transporting the handgun but I haven't found the root requirement.  So legal place to place would be OK but stopping and shopping wouldn't?  A car is more secure than a bike so one might "safely??" leave the locked container secure in a vehicle but might not have a secure locked spot on a bike.  Nor do I think that might be stretched to always having a hundgun with you in a locked container unloaded, even in a vehcile, and especially not out and about in a backpack.

A tank bag would be the motorcycle equivalent of a car's trunk, as would be saddle bags.  

A back pack, less so, as you are carrying it on your person, sort of.

In my opinion a tank bag would be the motorcycle equivalent to a glove compartment in a car/truck. There’s no putting saddle bags on my crotch rocket, so that’s out of the question.

If it's in a separate container, locked and unloaded, it shouldn't be an issue.

Yeah, I agree with you. I guess it would end up coming down to the type of cop.

Some bikes have a small, lockable compartment under the seat or elsewhere.  It might be large enough for a handgun.

One time, I walked to my local range carrying my handgun and ammo in a knapsack, unloaded and locked in its carrying case.  Afterwards, I realized that might be considered concealed carry.

Anyway, yours is an interesting question not directly addressed in the text of any firearms laws I have ever read.