We put it in our terms of service (and many companies that do signups over the web do, too). For big companies with strict privacy, they'll get in touch or let

We put it in our terms of service (and many companies that do signups over the web do, too). For big companies with strict privacy, they'll get in touch or let you know if they don't want you using it. That said, my strong preference is to highlight customers where we personally know someone there or have received very positive feedback (just in case someone wants a specific reference).