The Big House doesn't need fancy signs and gaudy, tawdry embellishment. It's an iconic structure whose beauty and awe is derived from its simplicity. It's minimalist approach is what makes it so special. You remember the halo? We don't need to bring that back.
We have commemorative plaques and displays throughout the stadium. Banners or signs are tacky (for football), and would do nothing but make us look insecure.