FMA, perhaps?
I study and teach (Certified Bachelor Instructor by GM Ramiro Estalilla, Jr.) FMA (Filipino Martial Arts), specifically, Estalilla Kabaroan Eskrima. Just about all FMA styles start out with simple weaponry typically a single stick. Just about anything can be used as a weapon if properly applied: a rolled up magazine, a pen, a mini-pump, a mini-mag flash light, etc. Just about anything can be used for self defense: a belt (not that anyone rides with one regularly), a handkerchief, etc. I've always thought that FMA styles make for great self defense arts, much like Krav Maga (though I'm still partial to FMA).
FMA can be seen in such movies as the Bourne Identity and the Boure Supremecy (Inosanto blend Kali) and The Hunted (Tommy Lee Jones and Benicio del Tory were given a crash course in Sayoc Kali). While primarily weapons based, FMA translates very easily into empty hand and improvised techniques: the rolled up magazine, the pen.
First things first: be aware of your surroundings.
Second: use only the least amount of force required: words, empty hand, weapon, etc; escalate accordingly, there is no reason to strike the head, if a rap on the wrist or elbow can end a confrontation. Likewise, recognise when you need to escalate.
Use common sense: remember, thieving, mugging low-lifes have more rights than victims. Sad but true.
Most street thugs and street crimes look for opportunity. If you fail to give them the opportunity, they will seek out something else to do or choose not to pursue you. Unfortunately, you can't always help the next guy that comes around. Listen to your common sense, it will help you.
IF you decide to carry a potentially lethal instrument/tool. KNOW how to use it. Don't just buy a knife thinking that brandishing it will automatically cause them to run. Like a gun, don't brandish anything as a threat, you need to be mentally and physically prepared to pursue that course of action. Take a self defense course; learn how to use a pocket stick/palm stick/yawara/kubotan. Remember, this is always the possibility that you will lose what you brandish and it may be used against you. IF you use force, you may also get sued for escalating the use of force beyond what may be considered reasonable (it may not be true but it can happen.) A pen can serve the same function as a kubotan but is legal to carry.
Carry a whistle - noise is your friend.
Property can always be replaced. Credit cards can always be cancelled. ID can always be reissued. Sure its a PITA but your safety is paramount.
Be safe. If you route makes you feel unsecure, change your route, the time you ride (if possible). Unfortunately, these are the times we live in.
Respectfully,
Anthony