The "infinity shield", according the brand website "symbolizes that the SOA is continually evolving to produce forward-thinking education and professional development opportunities. The shield represents a strong, fortified foundation, bound by standards and principles that advance your interests."
Wikipedia calls it an "impossible object".
So, quite simply, the essence of an actuary is represented by an infinite impossibility. Fitting, as much of the public still has no idea what actuaries do and some still doubt that actuaries actually exist. Why not be represented by a geometric symbol from the realm of mythology and legend?
Sources leaked some alternative designs that almost made the cut: