Others who really know lights will jump in here but to get started:
If the headlights are original early USA style, they are likely to be "AC" or maybe "AN" type lights. (The headlight model is marked on the glass). The original lights may have been changed to the more available "AJ" by a previous owner.
You ask about "Signal Bulb", assume this is the turn signal light.
The headlight Chrome Surround comes off the car by removing the single screw on the bottom of the Surround, then unhooking the Surround at the top. This exposes the light door, inner screws, and the bulbs.
The back of each type unit has a slightly different design. The bulbs will now be exposed or an inner cover may have to be unscrewed. The bulbs are bayonet type that come out by pushing in then turning.
Not sure what "weird shape" means except that modern bulbs (halogen, etc) have very small thin bulb bodies.
Take a look at the Tech Manual links below, they may help or wait till a better reply is posted.
If you have a photo of the light it may help.
http://www.sl113.org/wiki/pmwiki.php?n=Electrical.USLampIn case you have Euro lights:
http://www.sl113.org/wiki/pmwiki.php?n=Electrical.EuropeanLampRear of AJ light:
Download Attachment: AJ_Rear.jpg17.09 KB
Richard M, NYC