USB Token is a hardware device. For security reasons Digital Signature Certificates must be store into USB Tokens like Proxkey, Trustkey, Safenet 5100 etc. There are many manufacturer who produce USB Tokens for DSC. These USB Tokens can be accessable through Passwords. These tokens basically store DSC and ensures that private key can be accessable to you ONLY.
FIPS is Federal Information Processing Standards developed by US federal government for use in computer systems. FIPS is a standard for manudacturer to produce within guidelines. If product is being produced with FIPS Guidelines & found tested OK,product can be certified as FIPS Certified. As Digital Signature Certificate is very sensitive issue, hardware must be secured and certfied.