The real purpose of the GPO setting "RunLogonScriptSync" is to force it to run syncronously but it has the added side effect of making it visible. If visibility is your only objective, then take a look at the following:

Topic: FAQ Recommendation

See also, this Topic: Maximize login script window
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Give a man a fish and he will be back for more. Slap him with a fish and he will go away forever.