Ok, you shouldn't put the tag in to the script but you should call the script with it. {cell-signal-strength?{script: sh signalbar.sh}} This ties the execution of the script to changes in the property. The $percent variable in your script has the exact same value as the {cell-signal-strentgh} property at that time, so use that.
#!/bin/sh percent=$(qdbus --system com.nokia.csd /com/nokia/csd/csnet com.nokia.csd.CSNet.SignalStrength.SignalPercent) if [[ $percent -eq -1 ]] then echo -n "{{red}}Flugmodus an ✈" else if [[ $percent -ge 20 ]] then printf "{{yellow}}{{=$(($percent/100)).$((($percent%100)/10))$(($percent%10))}} $percent %" else if [[ $percent -le 19 ]] then printf "{{red}}{{=$(($percent/100)).$((($percent%100)/10))$(($percent%10))}} $percent %" fi fi fi