The SignalsDemo Expert Advisor uses the trade signals functions.
It shows the properties of the signals, available in client terminal, allows to modify the signal copy settings and subscribe or unsubscribe to the selected trade signal.
For work of the Expert Advisor you must login to MQL5.community in client terminal (enter your login in MQL5.community using Main menu->Tools->Options, tab "Community") and allow modification of the Signals settings in Experts Advisor options:
Fig. 1. Allow modification of Signals settings in Expert Advisor options
Fig. 2. Trade signals control in MetaTrader 4. SignalsDemo Expert Advisor