The icon menu graphics that display for the various signal styles are bitmap files saved to your C:\Program Files [(x86)]\Autodesk\AutoCAD {version}\Acade\ folder where AutoCAD Electrical's Insert Signal utilities and Drawing Properties tool can access them.
When a source or destination signal arrow is inserted it is cross-referenced. The source arrow has the reference for the destination arrow. The destination arrow has the reference for the source arrow. The cross-reference text can carry a prefix, for example “to” on a source arrow and “from” on a destination arrow. This prefix value is defined on the signal arrow library symbol. You can change the prefix by modifying the library symbol.
See the topic Source/Destination Wire Signal Arrow Symbols to determine the name of the signal arrow you want to modify.