签证签发后是什么?
这个问题问得有些怪,我猜大概是想问 “签证” (visa) 这个东西在正式旅行前是个什么东西吧? 这么说的话其实很简单: "Visa" is a piece of paper that says you're allowed to enter the country it's issued in. It tells customs which documents they need to check when you arrive, and how long they can keep those on their books once your stay has expired ("D" for duration of stay), all of this information being determined by where and with whom (who issued the visa) the visa was issued. A visa sticker or stamp is placed into your passport, indicating either its validity (which may be restricted from time to time depending upon who issues them), as well as sometimes specifying what documents are required at border control. For example:
The above US Visa stamped in my passport allows me entry to the USA provided I have a valid passport within its validity, a return/onward ticket, and sufficient funds to support myself during my visit(as well as other criteria). The document list shown also includes a requirement for proof of health insurance, but this doesn't show up on the visa itself because it is not relevant for determining whether someone can actually come into the United States. This is an example of what people refer to as an 'evidence of travel plan' requirement, rather than a 'documentary evidence of insuranc' one: you don't carry around that paperwork yourself; you prove you have bought it somewhere else instead. Similarly, some visas specify only a passport with no expiration date while others require it to expire less than three months after arrival. Neither shows up anywhere on the actual visa itself; these kinds of things vary according to the issuing agency and the regulations governing their use, so there isn't any easy way to generalize about such requirements. In short: if a visa does anything at all, it is usually just stating something like "This person has been granted entry permission into whichever territory we say here on this card," nothing more complicated than that, despite what most travelers think!
So what happens next? If you get a visa on entering the country, then it might as well become null and void right away since