Jet Streams on significant weather charts
 

Normally jet streams depicted on the high-level SWC are marked with the wind speed symbols (50, 10, 5 knot symbols) and the pressure altitude of the core. However, some have an additional piece of information that I do not know its meaning. Below the FL410 of the core for example, there would be for example 260/550. What do they stand for?

Take a look here for example: (Jet streams over Libya, Atlantic ocean and Caribbean and some others have this extra "thing" while others do not)
http://www.aviationweather.gov/data/..._06_CL_new.gif

Jet Depth: The vertical depths to the 80 knot wind field above and below the jet steam using flight levels. Jet stream vertical depth forecasts are included when the maximum speed is 120 knots or more.

Technical Implementation Notice 06-29 ... Displaying Jet Depth Information