Possible call tracking display locations.

[Proto definition ![GitHub](https://developers.google.com/site-assets/logo-github.svg)](https://github.com/googleapis/googleapis/blob/master/google/ads/googleads/v25/enums/call_tracking_display_location.proto)

| Enums ||
|---|---|
| ## `AD` | The phone call placed from the ad. |
| ## `LANDING_PAGE` | The phone call placed from the landing page ad points to. |
| ## `UNKNOWN` | Used for return value only. Represents value unknown in this version. |
| ## `UNSPECIFIED` | Not specified. |