Channels 6, 11, 26 and 28 are great indicators of AM skip activity in-band, as well as the out of band frequency 26.915 MHz / 26915 kHz and nearby channels. 26.915 is very popular in the southern USA for AM stations, along with 26.935 MHz, 26.955 MHz, 26.905 MHz and 26.815 / 26.835 MHz (channels 26 and 28 "down one band"). 26.915 is channel 36 "down one band" and 26.935 MHz is channel 38 "down one band" so that also makes sense. 38 LSB is used by locals (at least in my area) and that seems to be popular elsewhere too.
Channel 19 can also be a good indicator of skip activity, when the band really gets going you'll hear the crazy heterodyne of hundreds of truckers talking at once. Not to mention truckstop ladies of the evening (lot lizards) advertising their wares, truck washes, CB shops and other businesses advertising to truckers on 27.185 MHz AM with automated transmissions. There's a truckstop on Interstate 95 about 30 miles north of where I live and there's two CB shops nearby, both of which advertise on channel 19. I know one of them transmits in the 300-400 watt range with a base station antenna on channel 19, and will usually lock down the channel even when nearby truckers are transmitting with high power radios. I'm sure when the skip is rollin' that CB shop can be heard on top of lots of the other stations on channel 19.
Looking forward to an uptick in 11 meter activity.