Here are some LED Signs introduced in some of the EPs (e.g. Stadium LED Sign from Showtime) and show different images periodically in game.
I have tried to replace the default images with S3PE but it only works with the billboards and other static objects.
I'm really eager to know is here a way to make it display my own image? Thanks.

So I looked a bit around the mesh and I think that the textures you're looking for are seperated from the mesh self. I even think it's one of EA's VFX effects in some way. Here is what I found:
Version: 0x00000003
PublicChunks: 0x00000001
Unused: 0x00000000
--- CountedTGIBlockList: Resources (0x0) ---
---
--- ChunkEntryList: ChunkEntries (0x1) ---
--- ChunkEntries[0] ---
--- 0x63A33EA7-0x58000000-0x464F1066C7C42583 - ANIM ---
Version: 0x00000001
Framerate: 0,2000
--- TextureList: Frames (0x3) ---
[0]: DDS[0x0000AB38]
[1]: DDS[0x0000AB38]
[2]: DDS[0x0000AB38]


Now the important part is the:

--- TextureList: Frames (0x3) ---
[0]: DDS[0x0000AB38]
[1]: DDS[0x0000AB38]
[2]: DDS[0x0000AB38]

It shows that it is linked to 3 DDS files and so far I can see in TSRW, those are only a specular map, a multiplier map and a additive effect (the one with the stars). I cloned it in S3OC and it seems that only 2 DDS files share the '0x0000AB38' but there is still one out there that needs to share that same rule. I hope this helped you somehow! I'll keep looking for the texture and tell you if I come across it. ^-^

EDIT: I think I've got the file, and like I said, it was indeed seperated from the actual mesh. if you search with the name: signStadiumEP6 In S3PE with the package FullBuild_p12.package which you can find with this path: C:\Program Files (x86)\Electronic Arts\The Sims 3 Showtime\GameData\Shared\Packages (unless you've the sims installed on another location, but this should be the default location)

Thanks for your response, Greenplumbbob.
I'm sorry that I hadn't clarified my problems at the first post. I can find the texture files from the package file with S3PE before.
After extracting the texture files and editing, I import the files to a new package file. However, the objects still display the default images in game.
I working in this way usually to replace the texture of objects in game. However, it doesn't work with the LED Sign.
I've also tried to extract all files of the LED Sign and then imported to a new package file but no luck.
Thanks again.

yeah I was talking about those images. The ones you are finding look a bit like some dancing sim Advertisement in the sims 3. the path I showed you locates to those pictures you mean, and I don't mean the Diffuse/multiplier, specular map and the other texture with the stars.
I guess the led sign goes farther than a simple 'edit' but more like a default replacement/recolouring. Though, I'm not sure that, if you would change the image with yours, the other signs will display the same image you're using.
I don't think this will really help you out with the problem, but Pocci's blog has tons of useful tutorial, especially when it comes to tutorials I wished I saw sooner: http://poccisims3.blogspot.nl/2014/...eplacement.html