Applies a Tag to a content item for a specified user. If the tag text does not already exist, it is created. The newly created ID is accessible via the returned TagData. 

This method can be accessed through the Tags.asmx file located in:

~/Workarea/webservices/WebServiceAPI/Community/Tags.asmx

[SoapHeader("AuthHeader")]
[SoapHeader("RequestInfoHeader")]
[WebMethod(MessageName = "AddTagToContent with user and language", Description = "Applies a Tag to a piece of content.  If the tag text does not already exist, it is created.  The newly created Id is accessible via the returned TagData.")]
public TagData AddTagToContent(string tagText, long contentId, long userId, int languageId);

<SoapHeader("AuthHeader")>
<SoapHeader("RequestInfoHeader")>
<WebMethod(MessageName = "AddTagToContent with user and language", Description = "Applies a Tag to a piece of content.  If the tag text does not already exist, it is created.  The newly created Id is accessible via the returned TagData.")>
Public Function AddTagToContent(tagText As string, contentId As long, userId As long, languageId As Integer) As TagData