Message Board : Custom fields

Here is an example of the code needed: Note: this is just a quick example, you may have to modify it or change parts depending on your needs.

Step 1) Register your macro name space

using System;
using System.Collections.Generic;
using System.Linq;
using System.Web;

/// <summary>
/// Summary description for BPMacros
/// </summary>
using CMS.Base;
using CMS.MacroEngine;

[Extension(typeof(CustomMacroMethods))]
public class BPMacros : MacroNamespace<BPMacros>
{

}

[MacroNamespaceLoader]
public partial class CMSModuleLoader
{
    /// <summary>
    /// Attribute class that ensures the registration of custom macro namespaces.
    /// </summary>
    private class MacroNamespaceLoaderAttribute : CMSLoaderAttribute
    {
        /// <summary>
        /// Called automatically when the application starts.
        /// </summary>
        public override void Init()
        {
            // Registers "CustomNamespace" into the macro engine
            MacroContext.GlobalResolver.SetNamedSourceData("BPMacros", BPMacros.Instance);
        }
    }
}
Step 2)Create Macro Method
using CMS;
using CMS.CustomTables;
using CMS.DataEngine;
using CMS.DocumentEngine;
using CMS.EmailEngine;
using CMS.Helpers;
using CMS.MacroEngine;
using CMS.Membership;
using CMS.OnlineForms;
using CMS.SiteProvider;
using System;
using System.Collections.Generic;
using System.Data;
using System.Linq;
using System.Web;

[assembly: RegisterExtension(typeof(CustomMacroMethods), typeof(BPMacros))]
/// <summary>
/// Summary description for CustomMacroMethods
/// </summary>
public class CustomMacroMethods : MacroMethodContainer
{

    /// <summary>
    /// Returns a field for a user depending on the string fieldname passed in
    /// </summary>
    /// <param name="context"></param>
    /// <param name="parameters"></param>
    /// <returns></returns>
    [MacroMethod(typeof(string), "Returns particular field for specific user", 1)]
    [MacroMethodParam(0, "param1", typeof(int), "UserID")]
    [MacroMethodParam(1, "param2", typeof(string), "FieldName")]
    public static object BPUser(EvaluationContext context, params object[] parameters)
    {
        int UserID = ValidationHelper.GetInteger(parameters[0], 0);
        string returnVal = string.Empty;
        UserInfo ui = UserInfoProvider.GetUserInfo(UserID);
        if (ui != null)
        {
            try
            {
                returnVal = ui.GetValue(ValidationHelper.GetString(parameters[1], "")).ToString();
            }
            catch (Exception ex)
            {
                //macro error
            }
        }
        return returnVal;
    }
}

Step 3)Call Macro {% BPMacros.BPUser(53, "FullName")|(identity)GlobalAdministrator%}