Link has a video of the sign, but doesn't specify the exact location.
A large “Trump” sign that appeared overnight in the Sepulveda Pass hills near the 405 Freeway was promptly taken down by authorities Tuesday morning.
The sign was made of large white capital letters similar to those of the iconic Hollywood sign and was reportedly spotted just before 7 a.m.
There’s little information about who placed the sign, but Lauren Wonder, chief public information officer for the California Department of Transportation, said it was on private property.
https://www.latimes.com/california/story/2020-10-06/trump-sign-appears-and-swiftly-disappears-in-sepulveda-pass