This appeared in my gmail as a paid ad today (Email subscribers, click through to see the poison below):

I'm not a financial advisor.  There's probably money to be made in Bitcoin, although the SEC has issued investor warnings.

The vast, vast majority of your employees aren't qualified to evaluate Bitcoin as an investment option.  When ads like this pop up, I'm assuming they aren't offering Bitcoin as a speculative 5% of someone's portfolio - I'm assuming they want to cram all 100% of that rollover in Bitcoin for various reasons that have to do with money.

Many of your employees have 401ks parked with a previous employer.  25% know about Bitcoin and are interested in the hype.  1/5 of those would consider this ad.

It's worth you getting in front of this with a HR comms piece -  to let people know that ads are rolling encouraging 401k rollovers straight into Bitcoin and there's some danger via the SEC.  

Respect the game.