Not to the naked eye, but in at least one instance, astronomers have been able to detect optical flashes from the pulsar in the Crab Nebula as it goes about its business. The image of the optical pulsar has appeared in many textbooks used by undergraduates such as George Abell's Exploration of the Universe Third Edition, page 589. The photograph was taken by astronomers J. Miller and E. Wampler at Lick Observatory. The pulses are the synchrotron light emitted by the pulsar, and have the same period as the radio and X-ray pulses. If you were close to a pulsar, I suppose the light show would be quite fantastic....and lethal!