What is the red barb for in the NOAA weather briefing?
They do represent gusts:
From AviationWeather.gov:


Figure 1: Station Model Plot
In many cases, the data are plotted using standard symbols and
plotting models. Fig. 1 shows the station model used in the METAR and
TAF plots.

Ceil - Ceiling height in hundreds of feet. This represents the height of the lowest broken or overcast cloud layer.
Id - The 4 letter ICAO identifier for the site. KRFD is Rockford IL.
Windbarb - The wind barb. The stick points in the direction the winds are coming from. Each full barb represents 10 knots of wind.
Each half barb represents 5 knots. Red represents wind gusts. In this
case, you have winds from the SSW at 25 knots with gusts to 30 knots.


So for example, these:

The one on the left represents wind of 15 knots gusting 20, and the one on the right is 15 knots gusting 25.
Odd ones like this:

Mean 5 knots gusting 10. Why they don't overlay I'm not sure.