NEC 2008 400.22(E & F) For lamp cord, the following conventions are followed:
Polarized solid black, white or brown insulation
Ribbed, grooved or striped side is grounded (neutral), smooth side is ungrounded (hot).
Clear insulation lamp cord
Silver conductor is grounded (neutral), copper conductor is ungrounded (hot).
Grounded (neutral) goes to the threaded shell of the lamp and is wired direct without break to the wide blade of a polarized 2 prong plug or in the case of a suspended lamp, to the grounded (neutral) white wire. Switching goes in the ungrounded (hot) side. You never want the thread shell to be hot (switch in off position in the neutral side with intact filament).
If the conductors are both the same color, the insulation is a single color and the printing is on one conductor's insulation only without rib (feel it with your fingers) or stripe, then that will be your continuous marker and grounded (neutral) indicator. The whole idea on zipcord is that you have some definite identifier as to what is grounded (neutral) to keep a continuous connection and wire properly to the lamp socket and wall plug.
National Electrical Code
ARTICLE 400 Flexible Cords and Cables
II. Construction Specifications
400.22 Grounded-Conductor Identification. One conductor of flexible cords that is intended to be used as a grounded circuit conductor shall have a continuous marker that readily distinguishes it from the other conductor or conductors. The identification shall consist of one of the methods indicated in 400.22(A) through (F).
(E) Tinned Conductors.
One conductor having the individual strands tinned and the other conductor or conductors having the individual strands untinned for cords having insulation on the individual conductors integral with the jacket.
(F) Surface Marking.
One or more ridges, grooves, or white stripes located on the exterior of the cord so as to identify one conductor for cords having insulation on the individual conductors integral with the jacket.
Note: National Electrical Code (NEC) is the US standard and quoting it defines this answer as being for US electrical power. If your country differs, feel free to post your own answer with your country or jurisdiction identified.