I wouldn't call it a "personal endorsement" but then again, why would you use your signature space to advertise something you don't trust or believe in? Like advertising A bitcoin mixer or a gambling platform, yet you wouldn't ever use it in any scenario. To me, that's more like shilling (to talk about or describe someone or something in a favorable way because you are being paid to do it - source). Especially for us Bitcoiners, who have a chance to test out and use these platforms when they just get launched.