The International Prototype of the Kilogram is often called "IPK" and has been represented by a few “k” characters in publications since 1890. This character is based on the "k" from page 29 of the proceedings of the first General Congress on Weights and Measures, published in 1890. I asked the Unicode Consortium about designating characters for the IPK (and for the original meter) but was suggested to use the "Mathematical Bold Fraktur Capital K" (Unicode U+1D576 𝕶).
So that's one thing the IPK and the artist re-known as Prince have in common: no Unicode character for their name. After the redefinition, perhaps the IPK will become "the kilogram formerly known as the IPK.