Tibetan Script Puns

I know tibetans script comes from indian script. Looks very similar but why didnt they just use the indian script. Also, did tibetans ever use the chinese scripts?

In many ways, it seems likely to me that old tibetan did pronounce nearly all of them, as unusual as that may seem for modern Lhasa tibetan. But I met a native speaker who argues firmly against this idea and says that languages like ladakhi (who still pronounce many consonants that Lhasa tibetan doesnt) simply developed in a way that they started to pronounce those letters some day, while others stayed "original and true to old tibetan" which would essentially imply that old tibetan didn't pronounce the letters and simply added them in to distinguish homophones, but it makes no comments on why certain letters are silent and others arent, or how the silent letters affect vowel qualities (such as bod being phö) and tones in those tibetic langs that do not pronounce them, as opposed to those liek ladakhi who do (and dont have tones as well). Apart from this, the fact that some homophones are grammatically distinct forms of the same word (in the sense of verb tenses to be precise) and are written with distinct spelling for each form make me wonder if what the native speaker believes has any truth to it. And it doesn't help that the tibetan script was invented from brahmi, a highly phonetic script itself. Why would tibetans borrow such a script and use it completely differently from its phonetic values from the very start of writing their language?

So how was old tibetan most likely pronounced, and what were the likely phonological changes, so that I may know if there is truth to what the native speaker believes or if it is just to be taken with a grain of salt?

(The native speaker is not a linguist or a linguistics enthusiast, but a layman who seems rather well versed in his own language, even in native speaker terms)

EDIT: I take back what I said about the native speaker being well versed, he thinks tibetan doesnt have tones or pitch accent at all. Tibetan, as I understand, uses tones to actually distinguish words rarely, but every word still has a tone even if it may not necessarily help "distinguish"

I'm learning Tibetan and pretty much everything I write is in uchen script. I can't really read ume script, but I can recognise some letters.

When writing in daily life (letters etc), do most Tibetans write in ume script or in uchen? Doing a Google Image search for 'Tibetan handwriting' shows mostly ume, but is that accurate?

I’d like to ask if anyone could translate the phrase “Never give up” into Tibetan, using Tibetan script?

This is really bothering me so I’m hoping someone here will recognize it. Unfortunately, I couldn’t take a picture of it because it was on the back of a truck that quickly passed me.

Edit: I’ve checked every country flag, and it’s not a country flag.

It's currently written in the Roman but I assume they used a different script before the Christian missionaries or whoever reached the area and spread English.

I am referring to this post. The main source is this wikipedia article, which in turn cites

Goldwasser, Orly (Mar–Apr 2010). "How the Alphabet Was Born from Hieroglyphs". Biblical Archaeology Review (Washington, DC: Biblical Archaeology Society) 36 (1). ISSN 0098-9444. Retrieved 6 Nov 2011.

It's currently written in the Roman but I assume they used a different script before the Christian missionaries or whoever reached the area and spread English.