angular2 style guide - property with dollar sign?

The $ naming paradigm originated with Andre Saltz and suggests pluralizing all variable names that contain observables or streams.

getAll(): Observable<Zone[]>{
    let zone$ = this.http
      .get(`${this.baseUrl}/zones`, {headers: this.getHeaders()})
      .map(mapZone);
      return zone$;
  }

Another approach is to pluralize variable names that contain observables or streams with a unicode character that matches the last letter of the word. This addresses the issue with words that aren't pluralized with an "s".

mouse$ vs mic€

Neither of these naming conventions are in the official Angular style guide. Usage of one or the other (or none) is entirely dependent on personal preference.

$ suffix (popularized by Cycle.js) is used to indicate that the variable is an Observable. It could make it to the official style guide too but it's not there yet

Read more here : What does the suffixed dollar sign $ mean?

Update: Read more about the trailing “$” sign on Angular website here: https://angular.io/guide/rx-library#naming-conventions-for-observables