I've finally decided to spend a point in pickpocket, but after clicking on the pickpocket + sign and having spent the point, the pickpocket skill is empty as before, while it should show 1/5 of red. Question is: is it normal? Will the skill increase and remain invisible or the fact that it's invisible means it's messed up and not working?

Oh yeah, I'm wearing them. I'll give it a try and tell you the results. While we are speaking of penalties, where do I get a list of the abbreviations such as FR, NP ER and so on?

Here you go; I'm assuming you're familiar with stats (ST, IN, etc.), so here's the rest:

Resistances

AC - armor class (a.k.a. chance to avoid being hit)
DR - damage resistance (against general/physical damage)
ER - electrical resistance (against electrical damage)
FR - fire resistance (against fire damage)
MR - magick resistance (against spells and effects from magickal items)
PR - poison resistance (against poison damage)

Damage types

D - damage (physical); used on things like gauntlets which add to the base damage dealed by fists
ED - electrical damage
FD - fire damage
PD - poison damage
HT - "health", number of hit points or the amount of damage inflicted in combat
FT - "fatigue", number of fatigue points or the amount of fatigue damage inflicted in combat; weapons typically drain fatigue along with health, which can cause the target to go unconscious

Other stuff

MA - magickal aptitude
TA - technological aptitude
MSR - minimum strength requirement; wielding a weapon with MSR above your Strength stat inflicts penalties to accuracy/ToHit, larger difference leading to a larger penalty
NP - noise penalty on prowling; if you're a stealthy type, avoid this, as noise can cause you to be detected
RNG - range